Opto-computer methods and systems for through-light inspection of a glass container

Abstract

Opto-computer process and system for through-light inspection of a glass container. The invention relates to an opto-computer process and system for through-light inspection of a container (12), in which: - the container is illuminated by elementary emitting zones, each emitting polarized light having a polarization property of interest that varies according to a periodic variation law which, over a primary period (T1), follows a triangular variation as a function of the position of the elementary emitting zone along the primary direction (D1); - digital images with interposition are acquired with at least one camera, of a linear analyzer (30(n,k); 30.1, 30.2) having a polarization axis (Ak) given for a partial digital image (Ipk.m); - at least one raw primary refraction image (IR1) is calculated, each pixel of which is representative of the refraction undergone by the light.The system advantageously comprises a two-dimensional (16c) array of liquid crystal cells. Figure for the abstract: Fig. 1.

Description

Title of the invention: Opto-computer methods and systems for through-light inspection of a glass container. Technical field

[0001] The invention relates to opto-computer methods and systems for through-light inspection of a glass container using a digital camera, in particular for the purpose of computer-based detection of the presence of any defects in the glass constituting the container, in order to be able to identify whether such defects are disqualifying or not. Previous technique

[0002] There are numerous opto-computer methods for inspecting a glass container to detect defects, using one or more digital cameras, in which the detection and possible identification or classification of defects is carried out by computer analysis of one or more digital images acquired by these cameras. Some methods acquire a digital image in light reflected from the container. Other methods, such as those envisaged in the invention, operate in light transmitted through the container, the light source being in this case within the field of view of the digital camera used.

[0003] Defects in a glass container can be classified according to their specific or preferred interaction with the inspection light. Some defects may have several interactions depending on the characteristics of the light used, its direction, the shape and dimensions of the source, the observation conditions, etc. In other words, some defects can be detected with different types of inspection methods. Furthermore, some defects can be better detected and categorized by detecting them with different inspection methods, highlighting one or another interaction of the defect with the inspection light.

[0004] Certain defects have an absorbing character, either totally or partially absorbing. These defects thus appear opaque or dark when viewed in transmission. That is to say, light passing through a flawless glass wall undergoes what is called normal absorption, corresponding to the assumed homogeneous color and thickness of the glass wall. However, absorbing defects exhibit a local anomaly with absorption that is sometimes lower (bubble or thin) but generally higher than normal absorption. In the following, the term "absorption" will refer solely to the abnormal absorption of absorbing defects. Such defects include, in particular, inclusions in the glass, especially of ceramics or metals, and / or soiling (grease, etc.) on the glass. But such defects also include certain glazes (cracks) which would be oriented in the glass in such a way as to block the inspection light, mainly because the inspection light is then reflected in a direction which is not seen by the camera.

[0005] Some defects have a reflective character. This is the case for ordinary glazes, but also for certain defects on the ring surface, flaking, or metallic inclusions seen from certain angles.

[0006] Certain defects have a refractive character. This characteristic is mainly related to the interaction with light passing through one or two walls of the container. A wall has two opposing surfaces, each a thickness of the glass material. Each surface is an air / glass or glass / air interface, therefore a diopter that refracts the light passing through it. In the absence of a defect, the surfaces of the walls are substantially parallel, and refraction does not cause a visible deviation of the light rays passing through the container. A refractive defect is a defect that locally causes abnormal refraction, primarily when the defect manifests as differences in slope between surfaces or diopters of the wall(s). In the following, the term "refractive defect" will be used solely to designate deviations of light due to refraction specific to the location of so-called refractive defects.Refractive defects are those primarily detectable by the refractive anomalies they produce, particularly during through-light inspection. Typically, refractive defects include surface defects (folds, rivers) or glass distribution defects (bubbles, thins, compression rings), trapezoids, and fins.

[0007] Some defects have a diffusing character, in particular defects such as dirt, scratches, etc. It is noted that the diffusing character is often combined with an absorbing or refracting character.

[0008] Some defects have a birefringent character. Thus, some defects result in the presence of residual mechanical stresses in the material (sometimes called internal mechanical stresses or, particularly in English, "stress"). It is known that such defects can be detected by determining the change in the polarization state of light after it has passed through the container material and through any stress defects therein. Polarimetric cameras are now available to implement such methods.

[0009] Thus, depending on the nature of the defects one wishes to be able to detect in a given container, different inspection methods may be required. Even when considering inspection methods that operate using through-light, it may be necessary to use different illumination devices that provide inspection light with different light properties. Similarly, to analyze this light, one can requiring the implementation of different digital cameras, possibly with the interposition of a polarization analyzer having polarization analysis properties adapted to the process considered.

[0010] In order to be able to detect different defects, having different characteristics, it may therefore be necessary to implement complex systems.

[0011] Methods and systems are known in particular in which any refractive defects are detected by computer from a series of several digital intensity images acquired by a camera, in which anomalies in the image resulting from the total or partial refraction, by the defect, of the incident light projected by the light source are analyzed. The digital images used for such an analysis are therefore digital intensity images in which each pixel has a value proportional to the light intensity emerging from a point in the container optically corresponding to that pixel in the camera's optical system.

[0012] US4606634 describes a type of refractive defect detection that involves modifying the "angular spectrum" of an extended source. US4610542 describes a method employing a diffuse source exhibiting an intensity gradient such that the observed intensity is proportional to the slope of the refractive defects.

[0013] Other inspection methods adapted for the detection of refractive defects employ illumination devices which provide light which is sometimes called "structured", that is to say having an emitting surface, generally two-dimensional, which exhibits variations in intensity.

[0014] Thus, US4487322 describes a method in which a light source exhibits a variation (i.e., a gradient) of gray level (i.e., intensity) in the form of a ramp. Passing through the wall of the container deflects the light, and in the presence of a refracting defect, there is therefore a deformation of the ramp at the defect.

[0015] Other documents describe methods using light sources also described as "structured," but in which the light intensity varies periodically, with several periods of variation when traversing the useful inspection area seen by the digital camera in the background of the inspected area of ​​the container. EP0344617 and EP1006350 describe methods for observing, in transmission, the deformations of a pattern of stripes or shapes within a binary pattern, i.e., stripes or shapes that are either "white," with maximum light intensity, or "black," with minimum light intensity. Document EP2082216 describes a system that, with the same camera, acquires a first image with a uniform emitting surface, allowing for an appearance analysis, and a second image with a contrasting target pattern emitting surface.These methods, which employ binary periodic targets, pose a problem that, depending on the position of a defect. The position of the container relative to the target pattern in the background (as seen by the acquisition camera) affects the detection of defects. In particular, refractive defects located near a transition between two contracted shapes or stripes are poorly detected. This issue is partially addressed by the method described in document EP2558847, in which two images are taken with two targets of different colors, in opposite phase, and with a duty cycle other than 1, such that any refractive defect is contrasted and far from any target transition in at least one of the two images.

[0016] Documents FR2794241 and FR2794242 describe a method using a light source with a continuously varying intensity in the space between the extremes of dark and light. In this case, the variation increases the contrast of refractive errors, but the target itself is not detected. This method only detects strong refractive errors.

[0017] Documents EP3552001 and EP3679356 propose using a light source composed of areas emitting different colors and capturing color images. Refracting defects appear in the image as "artifacts" that do not have the same color as their surroundings. The refraction of refracting defects is revealed by color, while the absorption of absorbing defects remains revealed by drops in intensity. The drawback of this method is that it does not apply when the glass is tinted and blocks the transmission of certain colors. Moreover, as in the previous documents, the position of the defects relative to the color transitions of the background modifies the detection sensitivity.

[0018] Documents EP1980843 and FR2958040 each describe a reflective inspection method, called deflectometry, which employs lighting that presents, in the background of the object to be inspected, a light pattern whose intensity varies according to a sinusoidal variation law. The method involves collecting N images of the object by shifting the pattern by ir / N each time, and from the N images thus collected, calculating the phase at each illuminated point, which represents the position (modulo ji) in the sinusoid of the point source illuminating it. By assigning a phase value to each point of the illuminated object, if the calculated phase value is shifted relative to that which would be expected in the absence of a defect, it indicates that a defect is deflecting the light.A similar principle of deflectometry, this time in reflection, applicable to opaque objects, is described in the document "Another way of 'seeing' surface defects", Marie-Line Zani, MESURES 733 - MARCH 2001. The method of document EP1980843 consists of taking a phase image of the lenses and comparing it to reference phase images.

[0019] Document EP2875339 presents a transmission deflectometry method for moving bottles. It is noted that the objects to be inspected are moving When multiple images need to be acquired, the problem arises of the need to be able to superimpose the images pixel by pixel. Indeed, besides the simple displacement due to scrolling, which can generally be known, vibration phenomena cannot be ruled out, and these cannot be directly detected. Without perfectly superimposable images, detection inaccuracies are introduced.

[0020] Document WO2020 / 212014 describes a transmission inspection device for inspecting the side walls of containers transported by a conveyor. The device includes a lighting system with a light source and a downstream polarizer, and includes a polarimetric camera or a system of four cameras, each having a polarization analyzer with a polarization axis oriented in four directions, to simultaneously detect at least four different linear polarization directions.

[0021] Document WO2020 / 244815 describes a method for the optical inspection of containers, wherein the containers are transported to an inspection unit equipped with a lighting unit and a camera, wherein the lighting unit emits light from a light-emitting surface that is locally coded based on a polarization property, an intensity property, and / or a phase property. In WO2020 / 244815, the term "polarization property" means that the light emitted from different emission points of the light-emitting surface is emitted with different polarization directions in each case. In WO2020 / 244815, the term "polarization property" also means linear, elliptical, and / or circular polarization.For example, a polarizing filter with a continuously changing polarization curve or several polarizing filters with different orientations can be arranged in the light-emitting surface area. The document indicates that the camera may include a Sony IMX250MZR type sensor.

[0022] An object of the invention is to provide methods and systems that allow the detection of refractive defects at all points of an inspected area with homogeneous sensitivity throughout the inspected area, and with high sensitivity. Description of the invention

[0023] The invention therefore proposes an opto-computer method for inspecting a glass container moving along a trajectory using through-light, in which: - The method comprises illuminating the container by an illumination device including at least one two-dimensional emitting surface, which is arranged on one side of the displacement path and which is made up of emitting zones comments each emitting a polarized light having a polarization property of interest which varies according to a law of periodic variation as a function of the position of the elementary emitting zone in the emitting surface; - the method involves observing the container, by at least one digital camera having a two-dimensional photoelectric sensor comprising photoelectric elements, each comprising a photoelectric cell corresponding to a pixel in an image acquired by the digital camera, the at least one digital camera being located, with respect to the trajectory of movement, on the opposite side to that of the illumination device, so as to collect, by the at least one digital camera, emergent light emanating from the container and having passed through at least one wall thickness of the container; - the method comprises the acquisition, with at least one camera, of partial digital images, each containing an image of the same inspected area of ​​the container, each partial digital image having N partial pixels, each of which is the image of a corresponding elementary area of ​​the container, and each partial digital image being acquired with interposition, between the container and the photoelectric cells of at least one camera, of a linear analyzer presenting a given polarization axis for a partial digital image; - the acquisition includes the acquisition of at least one series comprising at least one first partial digital image and a second partial digital image, for which the polarization axes of the linear analyzers are distinct from each other, the partial digital images of the same series being superimposable such that each elementary area of ​​the inspected area of ​​the container is imaged by a corresponding partial pixel in each of the partial digital images of the series; - for a primary series, the partial digital images of the primary series each contain, in the background, the image of the same primary inspection portion of the emitting surface, the primary inspection portion being observed through the container by the digital camera, and, on the primary inspection portion of the emitting surface, the periodic variation law of the polarization property of interest emitted exhibiting, along a primary direction, a primary periodic variation, and exhibiting several primary periods over the extent of the primary inspection portion along the primary direction.

[0024] The method is characterized in that, over a primary period, the polarization property of interest emitted from the lights emitted by the elementary emitting zones of the primary inspection portion of the emitting surface follows a triangular variation as a function of the position of the elementary emitting zone along the primary direction), and in that the method comprises the computer calculation of at least one raw primary refraction image, from the partial digital images of the primary series, in calculating, for each of the elementary zones of an inspected zone of the container, a raw primary refraction pixel whose value is representative of the refraction undergone by the light having passed through at least one wall thickness of the container and emerging from the elementary zone, from the value of the corresponding partial pixels which are the image of the elementary zone in the partial digital images of the primary series.

[0025] Other optional features of such a process, taken alone or in combination, are described below.

[0026] In some cases, for the same inspected area of ​​the same container, the process includes the acquisition, for the primary series, of a third partial digital image and a fourth partial digital image for which the polarization axes of the linear analyzers are distinct from each other and distinct from the polarization axes of the linear analyzers for the first partial digital image and the second partial digital image of the primary series, preferably orthogonal to each other and offset by 45 degrees of angle from the polarization axes of the linear analyzers for the first partial digital image and the second partial digital image of the primary series.

[0027] In some cases: - for the same inspected area of ​​the same container, the acquisition includes the acquisition of at least one secondary series of partial digital images; - for the secondary series, the partial digital images each contain, in the background, the image of the same secondary inspection portion of the emitting surface, the secondary inspection portion being observed through the container by the digital camera, and, on the secondary inspection portion of the emitting surface, the law of periodic variation of the polarization property of interest emitted exhibiting, along a secondary direction of the emitting surface, different from the primary direction, a secondary periodic variation, and exhibiting several secondary periods over the extent of the secondary inspection portion along the secondary direction; - over a secondary period, the polarization property of interest emitted from the lights emitted by the elementary emitting zones of the secondary inspection portion of the emitting surface follows a triangular variation as a function of the position of the elementary emitting zone along the secondary direction; And, - the method includes the computer calculation of at least one raw secondary refraction image, from the partial digital images of the secondary series, by calculating, for each of the elementary zones of an inspected zone of the container, a raw secondary refraction pixel whose value is representative of the refraction affected by light having passed through at least one wall thickness of the container and emerging from the elementary zone, from the value of the corresponding partial pixels which are the image of the elementary zone in the partial digital images of the secondary series.

[0028] In some cases, partial digital images of the same series are acquired at the same instant.

[0029] In some cases: - at least one digital camera is a polarimetric digital camera, having a two-dimensional photoelectric sensor comprising photoelectric elements, each comprising a photoelectric cell in front of which is arranged an individual linear analyzer associated with the photoelectric cell of that photoelectric element, the photoelectric sensor comprising a number N of distinct groups of 4 contiguous photoelectric elements, the individual linear analyzers of which each have an axis of polarization, the four axes of polarization of a given group of 4 photoelectric elements forming two pairs of orthogonal polarization axes, the two pairs being offset from each other by 45 degrees of angle; And - the acquisition of the 4 partial digital images of the same series is carried out, with the photoelectric sensor of the polarimetric camera, by the acquisition of a master digital image containing an image of the container, the master digital image having a number 4*N of master pixels grouped into N composite pixels each corresponding to a group of contiguous photoelectric elements, each composite pixel having 4 master pixels each corresponding to one of the elements of the group of contiguous photoelectric elements corresponding to this composite pixel, and each master digital image comprising the 4 distinct partial digital images each having N partial pixels, the partial pixels of each of the partial digital images corresponding, for a given partial digital image, to the photoelectric elements of the photoelectric sensor whose individual linear analyzers have a common polarization axis for this partial digital image.

[0030] In some cases, for the same inspected area of ​​the same container, the primary series of partial digital images and the secondary series of partial digital images are acquired at different times.

[0031] In some cases, for the same inspected area of ​​the same container, the primary series of partial digital images and the secondary series of partial digital images are acquired with at least the same digital camera.

[0032] In some cases, the primary inspection portion and the secondary inspection portion correspond to two different polarization states, at different times, of the same inspection portion of the emitting surface.

[0033] In some cases: - Triangular variation is such that each primary period is divided into only two parts, an increasing part and a decreasing part. - in the increasing part, the polarization property of interest emitted is a linearly increasing function of the position of the elementary emitting zone along the primary direction, the polarization property of interest emitted increasing from a lower primary value to an upper primary value, - and, in the decreasing part, the emitted polarization property of interest is a linear decreasing function of the position of the elementary emitting area along the primary direction, the emitted polarization property of interest decreasing from the upper primary value to the lower primary value.

[0034] In some cases, the increasing part and the decreasing part of each primary period are of equal extent along the primary direction.

[0035] In some cases, the inspection portion of the emitting surface consists of elementary emitting zones, each emitting elliptically polarized light having an ellipticity ratio less than or equal to 0.7, and the polarization property of interest emitted from the light emitted by an elementary emitting zone is the orientation of the principal polarization axis of the light emitted by said elementary emitting zone.

[0036] In some cases, the lower, respectively upper, value of the polarization property of interest emitted is a lower angular value over one period, respectively upper value over one period, of the orientation of the principal polarization axis of the light emitted by the elementary emitting areas, the angular difference between the upper angular value and the lower angular value being at least 45 degrees of angle, preferably at least 70 degrees of angle.

[0037] In some cases, the primary inspection portion of the emitting surface consists of elementary emitting zones, each emitting light polarized according to an elliptical polarization having a phase shift between the two orthogonal components of the electric field vector of the emitted polarized light, and the polarization property of interest emitted corresponds to the phase shift between the two orthogonal components of the electric field vector of the emitted polarized light.

[0038] In some cases, the primary period is seen by the two-dimensional photoelectric sensor with a resolution, along the primary direction, of at least 15 partial pixels of the same partial digital image per primary period.

[0039] In some cases, the inspected area of ​​the container is seen by the two-dimensional photoelectric sensor with a resolution, along the primary direction, of at least 5 partial pixels of the same partial digital image per millimeter on the container.

[0040] In some cases, the value of a raw refraction pixel is calculated, for an elementary area of ​​the container, from the arctangent of a ratio between the values ​​of two corresponding partial pixels in the first partial image and the second partial image.

[0041] In some cases, the value of a raw refraction pixel is calculated, for an elementary area of ​​the container, from the arctangent of a ratio between, on the one hand, the difference in value of two corresponding partial pixels in the first partial image and the second partial image, and, on the other hand, the difference in value of the two corresponding partial pixels in the third partial image and the fourth partial image.

[0042] In some cases, the illumination device comprises, in the direction of light propagation, a primary two-dimensional source of diffuse light, an upstream linear polarizer having a polarization axis, and a two-dimensional array of liquid crystal cells.

[0043] In some cases, the method includes controlling the two-dimensional array of liquid crystal cells such that the polarized light from each of the liquid crystal cells has an elliptical polarization having, for each liquid crystal cell, the orientation of the principal polarization axis and / or a phase shift between the two orthogonal components of the electric field vector of the light from the liquid crystal cell, and, for the acquisition of the primary series of partial digital images, at least one of the orientation of the principal polarization axis and / or the phase shift follows a triangular variation as a function of the position of the liquid crystal cell along the primary direction.

[0044] In some cases, the method includes controlling the two-dimensional array of liquid crystal cells such that, for the acquisition of the secondary series of partial digital images, at least one of the orientation of the main polarization axis and / or the phase shift follows a triangular variation as a function of the position of the liquid crystal cell along the secondary direction.

[0045] In some cases, the method includes controlling the two-dimensional array of liquid crystal cells such that, successively, for the acquisition of the primary series of partial digital images of a given container, at least one of the orientation of the main polarization axis and / or the phase shift follows a triangular variation as a function of the position of the liquid crystal cell along the primary direction, and then such that, for the acquisition of the secondary series of partial digital images, at least one of the orientation of the main polarization axis and / or the phase shift follows a triangular variation as a function of the position of the liquid crystal cell along the secondary direction.

[0046] In some cases, the process includes a preliminary calibration step of the control of the two-dimensional matrix of liquid crystal cells.

[0047] In some cases, the method includes a refraction anomaly analysis step comprising a computer calculation step based on the raw refraction image.

[0048] In some cases, the refraction anomaly analysis step includes a gradient detection step in the raw primary refraction image along the primary direction.

[0049] The invention also proposes an opto-computer system for through-light inspection, using at least one digital camera, of a glass container moving along a trajectory, in which: - the system includes an illumination device comprising at least one two-dimensional emitting surface arranged on one side of the displacement trajectory and which consists of elementary emitting zones each emitting a polarized emitted light having a polarization property; - the system includes at least one digital camera having a two-dimensional photoelectric sensor comprising photoelectric elements, each comprising a photoelectric cell, the at least one digital camera being located, with respect to the trajectory of movement, on the opposite side to that of the illumination device, so as to collect, by the at least one digital camera, emergent light emanating from the container and having passed through at least one wall thickness of the container; - the system is configured to acquire, with at least one digital camera, at least one series comprising two partial digital images, each containing an image of the same inspected area of ​​the container, each partial digital image having N partial pixels, each of which is the image of a corresponding elementary area of ​​the container, and each partial digital image being acquired with interposition, between the container and the photoelectric cells of at least one digital camera, of a linear analyzer having a given polarization axis for a partial digital image, the polarization axes of the linear analyzers for the at least two partial digital images being distinct from each other, the partial digital images of the same series being superimposable such that each elementary area of ​​the inspected area of ​​the container is imaged by a corresponding partial pixel in each of the partial digital images of the series.

[0050] The system is characterized in that the illumination device comprises, in the direction of light propagation, a primary two-dimensional source of diffuse light, an upstream linear polarizer having a polarization axis, and a two-dimensional matrix of liquid crystal cells.

[0051] Other optional features of such a system, taken alone or in combination, are described below.

[0052] In some cases, the system includes means for controlling the two-dimensional matrix of liquid crystal cells such that the polarized light from each of the liquid crystal cells has an elliptical polarization having, for each liquid crystal cell, an orientation of the principal axis of polarization and / or a phase shift between the two orthogonal components of the electric field vector of the light from the liquid crystal cell, and the illumination device is controlled such that at least one of the orientation of the principal axis of polarization and / or the phase shift follows a variation as a function of the position of the liquid crystal cell along a primary direction of the emitting surface.

[0053] In some cases, the illumination device is controlled such that at least one of the main polarization axis orientation and / or phase shift follows a triangular variation as a function of the position of the liquid crystal cell along a primary direction of the emitting surface.

[0054] In some cases, the system includes, in the path of light between the two-dimensional array of liquid crystal cells and the linear analyzers for the at least two partial digital images, a quarter-wave delay plate which has a fast axis oriented parallel or perpendicular to the polarization axis of the upstream linear polarizer.

[0055] In some cases, the quarter-wave delay plate is arranged in the path of light between the two-dimensional matrix of liquid crystal cells and the container.

[0056] In some cases, the quarter-wave delay plate is arranged in the path of light between the container and the linear analyzers for at least two partial digital images.

[0057] In some cases, the system includes a computer computing unit programmed to perform the computer calculation of at least one raw primary refraction image, from the partial digital images, by calculating, for each of the elementary zones of an inspected zone of the container, a refraction pixel whose value is representative of the refraction undergone by the light having passed through at least one wall thickness of the container and emerging from the elementary zone, from the value of the corresponding partial pixels which are the image of the elementary zone in the partial digital images.

[0058] In some cases, the digital camera is a polarimetric digital camera.

[0059] In some cases, the control of the two-dimensional matrix of crystal cells liquids is synchronized with the acquisition, with at least one camera, of at least two partial digital images so as to: - acquire a primary series of at least two partial digital images when the two-dimensional array of liquid crystal cells is ordered in such a way that at least one of the orientations of the principal polarization axis and the phase shift follows a triangular variation depending on the position of the liquid crystal cell along the primary direction; - acquire a secondary series of at least two partial digital images when the two-dimensional array of liquid crystal cells is ordered such that at least one of the orientation of the principal polarization axis and the phase shift follows a triangular variation as a function of the position of the liquid crystal cell along a secondary direction different from the primary direction.

[0060] In some cases, the polarization axes of the linear analyzers for the at least two partial digital images are orthogonal to each other. Brief description of the drawings

[0061] [Fig-1] [Fig. 1] is a schematic perspective view illustrating a first type opto-computer system for through-light inspection of a container glass.

[0062] [Fig.2] [Fig.2] is a schematic perspective view illustrating a second type opto-computer system for through-light inspection of a glass container.

[0063] [Fig.3] Fig.3 is a schematic perspective view illustrating a third type opto-computer system for through-light inspection of a glass container.

[0064] [Fig.4] Fig.4 is a schematic top view illustrating another method of realization Development of an opto-computer system for through-light inspection of a glass container, comprising two digital cameras.

[0065] [Fig. 5] Fig. 5 is a schematic side view illustrating yet another mode of development of an opto-computer system for through-light inspection of a glass container, optimized more specifically for inspecting a bottom wall of the container.

[0066] [Fig. 6] Fig. 6 is a diagram illustrating an example of a periodic function triangular.

[0067] [Fig.7] Fig.7 is a schematic perspective view illustrating a principle of a sensor for a polarimetric digital camera.

[0068] [Fig.8] Fig.8 is a diagram illustrating an arrangement of linear analyzers polarization for a sensor for a polarimetric digital camera.

[0069] [Fig.9] Fig.9 illustrates a master image acquired by a digital camera. larimetric, comprising several partial images.

[0070] [Fig. 10] Figure 10 illustrates a flowchart for an opto-informatic process inspection using through-light of a glass container.

[0071] [Fig. 11] The [Fig. 11] is a diagram illustrating the principle of dimensioning certain parameters of a system for an opto-computer process of through-light inspection of a glass container, along a primary direction.

[0072] [Fig. 12] Figure 12 is a diagram illustrating the principle of dimensioning certain parameters of a system for an opto-computer process for through-light inspection of a glass container along a secondary direction. Description of embodiments

[0073] Figures 1 to 5 illustrate different optical systems 10 for inspecting defects in transparent, coloured or uncoloured glass container 12, for example a glass bottle or a glass jar.

[0074] In each case, the system 10 is designed to, and is capable of, implementing an opto-computer process for through-light inspection of a glass container using at least one digital camera 12. In certain embodiments, such as those illustrated in Figures 1 to 3 or in [Fig. 5], the system 10 may comprise a single camera 18, which in this case will advantageously be a single polarimetric digital camera 18 as described in more detail below. In some of these embodiments, such as that illustrated in [Fig. 4], the system 10 will comprise a set of several digital cameras, for example, two digital cameras 18.1, 18.2, the two digital cameras 18.1, 18.2 then being able to be conventional digital cameras, monochrome or color. In all cases, the digital camera(s) 18, 18.1, 18.2 each comprise a two-dimensional photoelectric sensor 22 having a two-dimensional array of photoelectric elements, each comprising a photoelectric cell. The digital camera(s) 18, 18.1, 18.2 each allow at least one digital image to be acquired of at least one area of ​​the container as it passes through the inspection position 13 of the system 10, the digital image thus acquired being used in the inspection process described below.

[0075] More specifically, the system 10 is designed to, and is capable of, implementing such a process in an industrial production line for glass containers and / or in an industrial automated transport line for glass containers, and / or in an industrial automated filling line for glass containers. In such lines, containers are transported, for example by a conveyor 14 of the line, along a travel path T, in at least one row of successive containers along the path. The rate at which containers travel in such a line can, for example, be between 150 and 1200 containers per minute.

[0076] The system 10 is designed and suitable for installation at a given station along such a line, so as to implement the opto-computer inspection process in light passing successively for each container 12 in the line of containers, at the time of the passage of the container 12 to the inspection location 13 of the system 10, location at which a container 12 must be placed to be inspected by the system 10.

[0077] At the inspection location 13 of the system 10, the circulation path of the containers 12 can be a straight path, or a curvilinear path. The inspection location 13 can be represented by a vertical axis A13 fixed relative to the system 10. For example, the container 12 can be considered to be located at the inspection location 13 when a principal axis A12 of the container 12, for example, an axis of symmetry of the container, or for example, an axis of revolution symmetry of the container, coincides with the fixed vertical axis A13 corresponding to the inspection location 13. In the examples illustrated in Figures 1 to 4, the system 10 is specifically designed to inspect the side wall of the container 12. As illustrated in [Fig. 5], the system 10 can be designed to inspect other parts of the container 12, for example, the bottom wall of the container 12.

[0078] The system 10 includes an illumination device 16 that delivers incident light onto the container 12 when the container is at the inspection location 13 of the system 10. In other words, the illumination device 16 delivers incident light towards the inspection location 13 of the system 10.

[0079] As a through-light inspection system, the illumination device 16 includes a primary light source 16a which is arranged in the field of vision of the digital camera(s) 18, 18.1, 18.2. Thus, at the time of its passage through the inspection location 13 of the system 10, the container 12 to be inspected is arranged, in the path of the incident light delivered by the illumination device 16, between the illumination device 16 and the digital camera(s) 18, 18.1, 18.2. In other words, the inspection location 13 of the system 10 is arranged between the illumination device 16 and the digital camera(s) 18, 18.1, 18.2 in the path of the incident light delivered by the illumination device 16. Thus, at least one digital camera 18, 18.1, 18.2 is located, relative to the displacement trajectory T, on the opposite side to that of the illumination device 16, so as to collect, by at least one digital camera 18, 18.1, 18.2, emergent light emanating from the container 12. To do this, the digital camera(s) 18, 18.1, 18.2 collect(s) the incident light emitted by the illumination device, after it has passed through the inspected area of ​​the container. The light collected by the digital camera(s) 18, 18.1, 18.2 has therefore interacted with at least one wall thickness of the container, often with two wall thicknesses of the container 12. In this interaction with the container, the light collected by the digital camera(s) 18, 18.1, 18.2 may have undergone, relative to the . light emitted by the illumination device, at least of the refraction that the systems and processes described below will seek to inspect.

[0080] Figures 1 to 4 illustrate systems 10 arranged to allow inspection of a side wall of a container such as a glass bottle 12. The conveyor 14 is, for example, a belt conveyor, on which the bottle 12 is placed bottom-first. In such systems, the light collected by the digital camera(s) 18, 18.1, 18.2 from the inspected area of ​​the container has therefore interacted with two wall thicknesses of the container 12.

[0081] In [Fig. 5], a system 10 is illustrated which is arranged to allow inspection of the bottom of a container 12 such as a glass bottle. The conveyor 14 is, for example, a belt conveyor comprising two opposing lateral belts, each of which rests on the two opposite sides of the bottle's side wall to hold it in place. The illumination device 16 is arranged on the bottom side of the bottle 12, perpendicular to the bottle's axis A12. The digital camera 18 is arranged on the other side of the bottle, oriented along its axis A12 so as to view the bottle's bottom wall through the bottle's upper opening, thus allowing for transparent inspection. In such a system, the light collected by the digital camera(s) 18, 18.1, 18.2 from the inspected area of ​​the container therefore interacted with only one wall thickness of the container 12

[0082] As will be understood from what follows, the illumination device 16 comprises at least one two-dimensional emitting surface 16s, which is arranged on one side of the displacement path T and is oriented towards the inspection location 13. The emitting surface 16s consists of elementary emitting zones, each emitting polarized light. As will be seen below, the illumination device 16 can be configured such that, for the acquisition of digital images intended for use in the process, the light emitted by each of the elementary emitting zones has a polarization property of interest that varies according to a periodic variation law depending on the position of the elementary emitting zone within the emitting surface. The incident light delivered by the illumination device 16 is therefore polarized light.

[0083] In the illustrated examples, the illumination device 16 comprises, in the direction of light propagation, a primary two-dimensional source 16a of diffuse light, an upstream linear polarizer 16b having a polarization axis A0, and a two-dimensional array 16c of liquid crystal cells 16c(i,j). The two-dimensional array 16c is a controlled array in the sense that each liquid crystal cell 16c(i,j) can be controlled such that, for a given polarized light at the cell input, at least one polarization property of the light exiting from the cell can be modified variably according to a control instruction applied to the liquid crystal cell 16c(i,j).

[0084] In certain embodiments, particularly those of Figures 1, 3, 4, and 5, the emitting surface 16s of the illumination device 16 is constituted by the surface of the two-dimensional matrix 16c of liquid crystal cells which is turned towards the inspection location 13.

[0085] On the other hand, in certain embodiments, such as that illustrated in [Fig.2], the illumination device 16 also includes a quarter-wave delay plate 16d which has a fast axis oriented parallel or perpendicular to the polarization axis AO of the upstream linear polarizer 16b. In the example of [Fig. 2], the quarter-wave delay plate 16d is part of the illumination device 16 and is arranged in the path of the light between the two-dimensional array 16c of liquid crystal cells and the inspection location 13, therefore between the two-dimensional array 16c of liquid crystal cells and the container 12 when the container 12 is located at the inspection location 13. In such a case, the emitting surface 16s of the illumination device 16 is constituted by the surface of the quarter-wave delay plate 16d which is turned towards the inspection location 13. It will be noted that when, as in the example of [Fig. 2], the quarter-wave delay plate 16d is part of the illumination device 16 and is arranged in the path of the light between the two-dimensional array 16c of liquid crystal cells and the inspection location 13, and therefore between the two-dimensional array 16c of liquid crystal cells and the container 12 when the container 12 is located at the inspection location 13. In such a case, the emitting surface 16s of the illumination device 16 is constituted by the surface of the quarter-wave delay plate 16d which is turned towards the inspection location 13. It will be noted that when, as in the example of [Fig. 2], the emitting surface 16s of the illumination device 16 is located in the illumination device 16c of ...[2], the quarter-wave delay plate 16d is part of the illumination device 16, the quarter-wave delay plate 16d can be directly attached to the two-dimensional array 16c of liquid crystal cells, thus forming a single component with the two-dimensional array 16c.

[0086] In both cases, elementary emitting zones of the emitting surface 16s can therefore be determined. In the first case, each elementary emitting zone of the emitting surface 16s is a liquid crystal cell 16c(i,j) of the two-dimensional array 16c of liquid crystal cells, or possibly a predefined group of cells. In the second case, each elementary emitting zone of the emitting surface 16s is an elementary zone of the quarter-wave delay plate 16d whose background, when viewed from the digital camera, is a liquid crystal cell 16c(i,j) of the two-dimensional array 16c of liquid crystal cells, or possibly a predefined group of cells.

[0087] Generally, the emitting surface 16s is the surface of the illumination device 16 which emits the incident light towards the inspection location 13, and each elementary emitting area of ​​the emitting surface 16s is an area which presents, at any time, as seen by the digital camera 18, 18.1, 18.2, an identical value of the polarization property of interest emitted over the entire elementary emitting area.

[0088] Optionally, a protective transparent glass cover can be placed in front of the emitting surface 16s, without altering the polarization properties of the light emitted by the illumination device 16. Similarly, a spectral filter and / or coloured filter can be positioned in the path of the light without altering the polarisation property of interest of the light emitted by the illumination device 16. The system works in the same way with or without the protective glass and with or without a spectral filter or coloured filter.

[0089] Preferably, the emitting surface 16s is flat and perpendicular to the optical axis of the digital camera 18, 18.1, 18.2.

[0090] Preferably, the primary light source 16a is an extended light source. For example, the dimensions of the illuminated surface of the primary light source 16a, perpendicular to an axis of incidence extending from the light source 16a to the inspection location 13, are larger than the corresponding dimensions of the area to be inspected on the container 12. For example, the light source 16a may comprise a two-dimensional array of light-emitting diodes and a diffuser. A diffuser may, for example, be in the form of a translucent and / or frosted plate. In such a case, the light-emitting diodes may optionally be controlled individually, or may be controlled only in groups, or may be controlled only globally, i.e., with a single control over the entire illuminated surface of the primary light source 16a.In general, the primary light source 16a, including any light-emitting diodes, can be controlled according to at least one or more parameters such as light intensity, on-time, off-time, etc. The light-emitting diodes may be composed of "multi-die" diodes of different colors, chosen according to the tint of the glass, and controlled to deliver variable monochromatic or polychromatic emission spectra.

[0091] Preferably, the incident light has an energy spectrum within a wavelength band between 250 nm and 1000 nm, the wavelength band having a width of less than 150 nm, preferably less than 100 nm. Preferably, therefore, the primary light source 16a delivers light with such an energy spectrum, even if it includes one or more filters. With such a narrow energy spectrum, the incident light, and therefore preferably the light delivered by the primary light source 16a, approaches monochromatic light.Furthermore, if a quarter-wave delay plate is used, which is generally only suitable for a specific wavelength or a narrow wavelength band around that specific wavelength, the induced delay is exactly one-quarter of the wavelength only for that specific wavelength or for a narrow wavelength band around that specific wavelength. In some embodiments, the energy spectrum of the... incident light presents an energy spectrum which can be adjusted, for example by adjusting the primary light source 16a or by implementing one or more filters in the illumination device.

[0092] It has been seen that the illumination device 16 can be configured such that the elementary emitting zones each emit a polarized light having an emitted polarization property of interest that varies according to a periodic variation law as a function of the position of the elementary emitting zone within the emitting surface. In the illustrated embodiments, this variation law of the emitted polarization property of interest is obtained by appropriate control of the two-dimensional array 16c of liquid crystal cells.

[0093] Such a two-dimensional 16c array of liquid crystal cells is a known component in the field of liquid crystal displays. Generally, such a two-dimensional 16c array of liquid crystal cells comprises two parallel glass plates with a liquid crystal-type material sandwiched between them. The two inner faces of the glass plates each have an electrode array, each opposing electrode pair defining a 16c(i,j) liquid crystal cell. Each electrode pair can be controlled by a control setpoint, for example, a voltage setpoint, to generate, in the 16c(i,j) liquid crystal cell defined by the electrode pair, an electric field that acts on the orientation of the liquid crystals in the cell.Depending on their orientation within the cell, which is determined by the voltage control between the two electrodes of this cell, the effect of the liquid crystals on the polarization of the light passing through the 16c(i,j) liquid crystal cell varies. Thus, by varying the voltage between the two electrodes associated with the 16c(i,j) liquid crystal cell, the effect of the liquid crystals on the polarization of the light passing through each 16c(i,j) liquid crystal cell is varied.

[0094] It is recalled that, in the illustrated examples, the upstream linear polarizer 16b is provided in the path of the light, upstream of the two-dimensional matrix 16c of liquid crystal cells, so that the light which enters each liquid crystal cell 16c(i,j) is linearly polarized light along a polarization axis which is defined by the upstream linear polarizer 16b, and whose two orthogonal components of the electric field vector are without initial phase shift.

[0095] The action of the liquid crystals of the cell on the polarization of the light passing through the liquid crystal cell 16c(i,j) will notably transform this incoming light into an output light which will be: - in the case of certain two-dimensional array liquid crystal cell technologies, linearly polarized light having a polarization axis that will have undergone an angular shift, i.e. the result of a rotation, of the orientation 0c ( z, / ) of the polarization axis with respect to the polarization axis AO defined by the upstream linear polarizer 16b, the orientation 0c( z, j) of the polarization axis with respect to the polarization axis AO defined by the upstream linear polarizer 16b then being variable as a function of the voltage control between the two electrodes associated with the liquid crystal cell 16c(i,j); - more generally, in the case of other two-dimensional liquid crystal cell matrix technologies, elliptically polarized light, this polarization being characterized on the one hand by an orientation 0c(z, j) of a principal axis of the polarization ellipse (hereinafter referred to as the principal polarization axis), and on the other hand by a phase shift (pl6c(i, j)) between the two orthogonal components of the electric field vector of the light passing through it, the phase shift <pl6c(z, j) étant alors variable en fonction de la commande en tension entre les deux électrodes associées à la cellule à cristaux liquides 16c(i,j).

[0096] In reality, most technologies will fall within the general case in which the action of the cell's liquid crystals on the polarization of the light transforms this incoming light into an elliptically polarized output light, characterized both by an orientation 0c(z,j) of the principal axis of the polarization ellipse exhibiting an angular offset with respect to the polarization axis defined by the upstream linear polarizer 16b, which will vary according to the voltage control between the two electrodes associated with the liquid crystal cell 16c(i,j), and on the other hand by a phase shift <pl6c(ï, j) qui variera aussi en fonction de la commande en tension entre les deux électrodes associées à la cellule à cristaux liquides 16c(i,j).However, some technologies will generate, depending on the voltage control between the two electrodes associated with the liquid crystal cell 16c(i,j), a comparatively greater variation in the angular shift of the orientation 0c(z,j) of the principal axis of the polarization ellipse and, conversely, a comparatively smaller variation, or even small enough to be negligible, in the phase shift r / H 6ct7,j). It has appeared that this is, for example, the case with TN (“Twisted Nematics”) technology.Conversely, depending on the voltage control between the two electrodes associated with the 16c(i,j) liquid crystal cell, other technologies will generate a comparatively larger variation in the phase shift (pl 6c(z, j)), and, in comparison, a comparatively smaller variation, even small enough to be negligible, in the angular shift of the orientation 0c(z, j) of the principal axis of the polarization ellipse. It has appeared that this is, for example, the case with ECB (Electrically Controlled Birefringence) technology.

[0097] It is recalled that, in polarized light, the two vector components, preferably orthogonal, of the electric field of the light at a given point, at a given instant, completely define the orientation of the electric field at that given point and at that given instant. The figure described over time by the electric field at a given point is then: - for linear polarization, a straight line segment that defines the orientation of the linear polarization axis; - for elliptical polarization, an ellipse in which we can define a major axis of the ellipse, which will hereafter be called the principal axis of the ellipse or principal axis of polarization, and a minor axis; - for circular polarization, a circle.

[0098] For elliptically polarized light, the ratio of ellipticity, or in short "ellipticity", can be defined as the ratio between the minor axis of the polarization ellipse and the major axis of the polarization ellipse, the latter being the principal axis of polarization.

[0099] In the present text, linearly polarized light will be considered a special case of elliptically polarized light, with in this special case: - a flattened polarization ellipse reduced to a segment, for which the principal polarization axis, which is the segment formed by the flattened ellipse, is simply the linear polarization axis of linearly polarized light; - a zero phase shift between the two orthogonal components of the electric field vector of light.

[0100] In the present text, circularly polarized light will be considered a special case of elliptically polarized light, with the following in this special case: - a polarization ellipse which is a circle; - a phase shift between the two orthogonal components of the electric field vector of light which is equal to 90 degrees of angle.

[0101] Consequently, the concept of elliptically polarized light contains that of linearly polarized light. For linear polarization the ellipticity ratio is 0, and for circular polarization the ellipticity ratio is 1.

[0102] It can therefore be considered that each liquid crystal cell 16c(i,j) of the two-dimensional 16c matrix of liquid crystal cells induces, in linearly polarized incoming light, which is here linearly polarized light, as a function of the voltage control between the two electrodes associated with the liquid crystal cell 16c(i,j): - a variable angular shift in the orientation of the principal polarization axis, which results in a variation of the orientation 0c(i,j) of the principal polarization axis of the light exiting the liquid crystal cell 16c(i,j) as a function of the voltage control between the two electrodes associated with the 16c(i,j) liquid crystal cell; - and / or a variation of a delay, or phase shift ^16^(4 j), between the two orthogonal components of the electric field vector of the light coming out of the liquid crystal cell 16c(i,j).

[0103] Thus, this orientation 0c(z,j) and / or this phase shift ç>l6c(4j) can be controlled by controlling the voltage between the two electrodes associated with the liquid crystal cell 16c(i,j). Thus, by controlling the voltage between the electrodes of each liquid crystal cell 16c(i,j), the two-dimensional matrix of liquid crystal cells can be configured such that the polarized light emitted from each of the liquid crystal cells exhibits an elliptical polarization having, for each liquid crystal cell 16c(i,j), at least one controlled polarization property among: - an 0c ( Z, / ) orientation controlled from the main polarization axis; - and / or a controlled phase shift ç>16ü(z, j) between the two orthogonal components of the electric field vector of the light from the liquid crystal cell 16c(i,j).

[0104] It should be noted that the arrangement of a linear polarizer upstream of a two-dimensional array of liquid crystal cells is an inherent technique in the manufacture of liquid crystal displays. Thus, those skilled in the art can implement, for the realization of the illumination device 16, and in particular with regard to the association of the upstream linear polarizer 16b with the two-dimensional array 16c of liquid crystal cells, techniques and design rules that are commonly used in the field of liquid crystal displays.Conversely, it will be noted that, contrary to a usual construction of liquid crystal displays, the illumination device 16 does not include a linear polarizer downstream of the two-dimensional array of liquid crystal cells, in particular no linear polarizer in the path of light between the two-dimensional array 16c of liquid crystal cells and the inspection location 13 where the container 12 to be inspected is to be placed.

[0105] In the two-dimensional array 16c of liquid crystal cells, the liquid crystal cells 16c(i,j) are generally arranged in a two-dimensional lattice in the plane of the array, with a perpendicular column (i) and row (j) arrangement. Generally, it is noted that the polarization axis A0 of the upstream linear polarizer 16b is preferably oriented at 45° with respect to the perpendicular columns and rows of liquid crystal cells 16c(i,j) of the two-dimensional array 16c.

[0106] Preferably, the system 10 comprises control means for the two-dimensional matrix of liquid crystal cells, capable of controlling each cell 16c(i,j) individually, thus individually controlling as many cells as the number of columns multiplied by the number of rows. In such a case, an elementary area of ​​the emitting surface 16s will correspond to a cell 16c(i,j) of the two-dimensional matrix of liquid crystal cells. However, in some embodiments, the system 10 could be provided with control means that are not capable of controlling each cell 16c(i,j) individually, but only of individually controlling groups of cells, for example, rows 16c(i) of cells, columns 16c(j) of cells, or sets of adjacent cells.In such a case, an elementary emitting zone will correspond to one of these columns, one of these rows, or one of these sets of liquid crystal cells. For the remainder of the description, we will consider the case of control means that are capable of individually controlling each liquid crystal cell 16c(i,j).

[0107] In all cases, the system is expected to be capable of configuring at least a portion of the two-dimensional matrix of liquid crystal cells such that the polarized light from each of the liquid crystal cells exhibits an elliptical polarization having, for each liquid crystal cell 16c(i,j), a controlled orientation 0c(i,j) of the principal polarization axis and / or a controlled phase shift ç?16c(z,j) between the two orthogonal components of the electric field vector of the light from the liquid crystal cell 16c(i,j). The portion that can be thus controlled, or the portion that is actually thus controlled, corresponds to a portion called the inspection portion of the emitting surface 16s. This portion is also two-dimensional.

[0108] It therefore appeared that, depending on the voltage control applied to the electrodes of a given 16c(i,j) liquid crystal cell, it was possible, when light passes through the liquid crystal cell, the light being linearly polarized and therefore without phase shift at the entrance to the 16c(i,j) cell, to induce a controlled 0c( z, j) orientation of the main polarization axis and / or a controlled phase shift between the two orthogonal components of the electric field vector of the light coming from the 16c(i,j) liquid crystal cell.

[0109] In technologies that allow it, for example the "TN" technology, the orientation 0c(i,j) of the main polarization axis can thus vary, depending on the control applied to the electrodes, from an initial value, corresponding to the case where no voltage is applied to the electrodes of the liquid crystal cell 16c(i,j), to a final value, corresponding to the case where a maximum voltage is applied to the electrodes of the 16c(i,j) liquid crystal cell. In some of these technologies, for example the "TN" technology, the initial value of the 0c(i,j) orientation of the principal polarization axis is 90° to the orientation of the polarization axis of the incoming light, and therefore 90° to the orientation of the polarization axis of the upstream polarizer. It appears that, depending on the characteristics of the two-dimensional 16c liquid crystal cell array, the final value of the 0c(i,j) orientation of the principal polarization axis of the light from the liquid crystal cell, corresponding to the maximum voltage applied to the liquid crystal cell electrodes, can reach an angular offset from the initial value of at least 30 degrees, preferably at least 45 degrees, and more preferably 70 degrees.

[0110] In technologies that allow it, for example the "ECB" technology, the phase shift <pl 6c(L / ) peut ainsi varier, en fonction de la commande appliquée aux électrodes, d’une valeur initiale, dans certains cas une valeur nulle, correspondant au cas où aucune tension n’est appliquée aux électrodes de la cellule à cristaux liquides 16c(i,j), à une valeur finale, dans certains cas une valeur maximale, correspondant au cas où une tension maximale est appliquée aux électrodes de la cellule à cristaux liquides 16c(i,j).It appears that, depending on the characteristics of the 16c two-dimensional liquid crystal cell array, the difference between the initial and final phase shift values ​​between the two orthogonal components of the electric field vector of the light emitted by the liquid crystal cell, corresponding to the maximum voltage applied to the liquid crystal cell electrodes, can reach a value in the range of 45 to 90 degrees. At least some of the two-dimensional liquid crystal cell arrays of "ECB" technology exhibit such behavior.

[0111] It is noted that the correlation between on the one hand the voltage applied to the electrodes of the liquid crystal cell 16c(i,j) and on the other hand the value of the orientation 0c( z, j) of the main polarization axis and / or the phase shift (pl6c(i, j) can be a positive correlation, if the two vary in the same direction, or a negative correlation, if the two vary in opposite directions.

[0112] Similarly, it appeared that, in both cases, the variation of the orientation 0c(i,j) of the principal polarization axis and / or the phase shift ç?16c(z,j) induced in a light, initially linearly polarized and passing through the liquid crystal cell 16c(i,j), is a continuous function of the voltage applied to the electrodes of this liquid crystal cell 16c(i,j). On the other hand, it also appeared that the variation of the orientation 0c(i,j) of the principal polarization axis and / or the phase shift <pl 6c(i. j) induit dans une lumière, initialement polarisée linéairement et The voltage across the 16c(i,j) liquid crystal cell is not necessarily a linear or affine function of the voltage applied to the electrodes of the 16c(i,j) liquid crystal cell. However, it is possible, at least through a preliminary calibration procedure, to establish a conversion function that allows us to determine the value of the orientation 0c(i,j) of the principal polarization axis and / or the induced phase shift ç>16c(z,j) as a function of the voltage applied to the electrodes of the 16c(i,j) liquid crystal cell. In other words, it is possible, at least by a preliminary calibration procedure, to determine what voltage value must be applied to the electrodes of the 16c(i,j) liquid crystal cell to obtain an orientation 0c(i,j) of the main polarization axis and / or a desired induced phase shift qA6c(L / ) of initially linearly polarized light passing through the 16c(i,j) liquid crystal cell.An example of a calibration method will be given later.

[0113] The system 10 comprises control means 100, an example of which is symbolically illustrated in [Fig. 1] and [Fig. 4]. These control means 100 may include at least one computing unit, for example a standard computer 110. They may include one or more electronic interface unit(s) 120 for the digital camera(s) 18, 18.1, 18.2, at least part of which may be integrated into the digital camera(s). The control means 100 may include an electronic control unit 130 for driving the illumination device 16, in particular for driving the primary light source 16a and / or the two-dimensional array 16c of liquid crystal cells. The control means 100 may therefore include one or more microprocessors, one or more microcontrollers, one or more electronic memory units, and one or more display interfaces (screen, projector, holographic display, etc.).), input (keyboard, mouse, touchpad, touchscreen, etc.), and / or communication (USB, Ethernet®, Wi-Fi®, Bluetooth®, Zigbee®, etc.). The control means 100 may include a computer network sharing data between different elements of the control means, with one or more other computers on the network, or with other networks, for example via an internet protocol or Ethernet®.In addition to being connected to the digital camera(s) to collect and record the master / partial images (as defined below), and to the lighting device 16 to control it and possibly acquire operating data, the control means 100 may include or be connected to sensors providing information on container movement speed, the presence of a container at the inspection station, or other installation status information, and / or to installation actuators (conveyors, ejectors, etc.). The control means 100 may implement one or more software programs. stored and / or executed locally or remotely, including on one or more remote computer servers. This software preferably comprises one or more software programs designed to implement the computer steps of the process according to the invention.

[0114] Since the emitting surface 16s is two-dimensional, two distinct directions can be defined within its extent, in particular two orthogonal directions, one of which can be arbitrarily designated as the primary direction Dl. It will be seen that a secondary direction D2 can also be defined, different from the primary direction Dl, preferably orthogonal to the primary direction Dl. For example, the primary direction Dl can be a direction parallel to the axis A12 of the container 12 to be inspected, and therefore parallel to the fixed axis A13 corresponding to the inspection location 13. In such a case, the secondary direction D2 can be a direction oblique to the axis A12 of the container 12 to be inspected, for example inclined at an angle in the range of 30 to 60 degrees to the axis A12 of the container 12, or orthogonal to the primary direction Dl, and therefore orthogonal to the axis A12.

[0115] The use of a two-dimensional 16c array of controllable liquid crystal cells is particularly advantageous because it allows for the easy creation of incident light conditions having at least one polarization property that varies on the emitting surface 16s, thus creating a pattern of variation of at least one polarization property, including a pattern of complex variation and / or a pattern of gradual and continuous variation. Controlling the two-dimensional 16c array of liquid crystal cells makes it easy to switch from a first pattern of variation of at least one polarization property on the emitting surface 16s to at least a second pattern of variation of the same polarization property on the emitting surface 16s and / or a second pattern of variation of a different polarization property on the emitting surface 16s.This transition from one variation "target" to another can be carried out at a significant frequency, greater than 1 Hz, generally greater than 10 Hz, often greater than 100 Hz.

[0116] In general, it will be possible to obtain, through the use of a two-dimensional 16c matrix of liquid crystal cells, a variation "target" in which a polarization property, for example the 0c(i,j) orientation of the principal polarization axis and / or the phase shift <p!6c(i, j) entre les deux composantes orthogonales du vecteur de champ électrique de la lumière issue de la cellule à cristaux liquides 16c(i,j) suit une variation qui soit une fonction périodique de la position de la cellule à cristaux liquides 16c(i,j) considérée selon une direction, cette fonction étant de préférence une fonction « non-constante » sur tout intervalle compris dans une période. De même, une telle fonction sera de préférence également continue sur une période, et, encore plus Preferably, continuous over several periods, therefore without a jump between two periods. For example, such a variation could be a sinusoidal type variation, a linear or affine function over each period, etc. We will see that, for the implementation of a preferred method, such a variation will be a triangular variation as defined below.

[0117] In particular, the system 10 is capable of configuring at least a portion of the two-dimensional matrix 16c of liquid crystal cells such that at least one of the two polarization properties, among the orientation 0c(i,j) of the principal polarization axis and / or the phase shift ^16c(z, / ) between the two orthogonal components of the electric field vector of the light from the liquid crystal cell 16c(i,j) follows a variation, in particular a triangular variation, as a function of the position of the liquid crystal cell 16c(i,j) considered along the primary direction Dl.

[0118] In all the systems that will be described, the inspection portion of the emitting surface 16s can be considered to consist of elementary emitting zones 16s(i,j), each emitting elliptically, or even linearly, polarized light. The light emitted by an elementary emitting zone has two polarization properties, each of which can be the polarization property of interest. The first of these two polarization properties is the orientation of the principal polarization axis of the light emitted by said elementary emitting zone 16s(i,j), which can also be referred to hereafter as the polarization orientation of interest 6s(i,j) (sometimes also simply called the polarization direction).The second of these two polarization properties, which can be the polarization property of interest, corresponds to the phase shift j) between the two orthogonal components of the electric field vector of the emitted polarized light.

[0119] Depending on the embodiments of the system 10, we will describe different systems 10 belonging either to a first family of embodiments, implementing more particularly, as a variation of the polarization property of interest emitted, a variation of the orientation 0s( z, j) of the principal polarization axis of the light emitted by each elementary emitting zone 16s(i,j) of the emitting surface 16s, or to a second family of embodiments, implementing more particularly, as a variation of the polarization property of interest emitted, a variation of the phase shift (ps^i, j) between the two orthogonal components of the electric field vector of the light emitted by each elementary emitting zone 16s(i,j) of the emitting surface 16s.

[0120] In the first family of embodiments, we find a first type of embodiment in which the emitting surface 16s is the surface of the matrix bi 16c-dimensional liquid crystal cells, and each elementary emitting zone 16s(i,j) is therefore directly determined by an associated liquid crystal cell 16c(i,j). Thus, for embodiments of this first type, belonging to the first family of embodiments, the orientation 0c( / . / ) of the principal polarization axis induced by a liquid crystal cell 16c(i,j) corresponds directly to the orientation 0s( 4 / ) of the principal polarization axis, with therefore 0S ( i, j) = 0c ( i, j ) • For this first type of embodiment, the inspection portion of the emitting surface 16s is therefore made up of elementary emitting zones 16s(i,j) each emitting light polarized according to an elliptical polarization having an orientation 0s( j) of the principal polarization axis.

[0121] The systems 10 of Figures 1, 4, and 5 are examples of systems 10 of a first type belonging to the first family of embodiments, implementing more particularly, as a variation of the emitted polarization property of interest, a controlled variation of the orientation 0s( (, j) of the principal polarization axis of the emitted polarized light. Such systems will, for example, be advantageously implemented in the case where the technology of the two-dimensional array 16c of liquid crystal cells generates, as a function of the control applied to the liquid crystal cell 16c(i,j), a comparatively larger variation of the angular shift (as defined above) of the orientation of the principal axis of the polarization ellipse (for example, with the use of "TN" type liquid crystal cells).In this first type, the polarization property of interest emitted is therefore directly the orientation 0c( i, j) = 0s( i, j) of the principal polarization axis of the light coming from the liquid crystal cell 16c(i,j) and therefore emitted by the elementary emitting area.Thus, the control means 100 of the two-dimensional matrix 16c of liquid crystal cells will be able to configure the latter in such a way that the polarized light from each of the liquid crystal cells 16c(i,j), and therefore from each elementary emitting zone 16s(i,j), has an elliptical polarization having, for each liquid crystal cell 16c(i,j) and therefore for each elementary emitting zone 16s(i,j), an orientation 0s(i,j) = 0c(i,j) controlled from the principal polarization axis of the light from the liquid crystal cell 16c(i,j) and therefore emitted by the elementary emitting zone, which follows a variation, in particular a triangular variation, as a function of the position of the elementary emitting zone 16s(i,j) along the primary direction Dl. .

[0122] It should be noted that, for systems of the first family of embodiments, implementing more particularly, as a variation of the polarization property of interest emitted, a controlled variation of the orientation 0s(i,j) of the principal polarization axis of the emitted polarized light, a preferred choice will be made Illumination device 16 in which the polarized light emanating from each of the elementary emitting zones 16s(i,j) exhibits elliptical polarization having an ellipticity ratio less than or equal to 0.7, preferably as low as possible, or even zero. This will allow a more precise determination of the orientation of this principal polarization axis.

[0123] A second type of embodiment, also belonging to the first family of embodiments implementing more particularly, as a variation of the emitted polarization property of interest, a controlled variation of the orientation 0s( z, / ) of the principal polarization axis of the emitted polarized light, is illustrated by the example in Figure 2. In this example, the illumination device 16 comprises, downstream of the two-dimensional array 16c of liquid crystal cells, a quarter-wave delay plate 16d which is part of the illumination device 16 and which is arranged in the path of the light between the two-dimensional array 16c of liquid crystal cells and the inspection location 13. In such a system, the emitting surface 16s is then the surface of the quarter-wave delay plate 16d facing the inspection location 13.In such a system, each elementary emitting zone 16s(i,j) is a region of the surface of the quarter-wave delay plate 16d, this region being defined as the region which, seen from the digital camera 18, is seen with, in the background, a liquid crystal cell 16c(i,j) of the two-dimensional matrix 16c. Each elementary emitting zone 16s(i,j) is therefore associated with a liquid crystal cell 16c(i,j) of the two-dimensional matrix 16c.The system in Figure 2 will, for example, be advantageously implemented in the case where the technology of the two-dimensional matrix 16c of liquid crystal cells generates, rather, depending on the control applied to the liquid crystal cell 16c(i,j), a comparatively greater variation of the phase shift ç?l 6c(i,j) between the two orthogonal components of the electric field vector of the light from the liquid crystal cell 16c(i,j) (for example with the use of "ECB" type liquid crystal cells).Now, in a system 10 constructed in this way, ensuring that the fast axis of the quarter-wave delay plate 16d is parallel or perpendicular to the polarization axis AO of the upstream linear polarizer 16b, the phase shift <pl 6c(i, j) induit par une cellule à cristaux liquides 16c(i,j) de la matrice bidimensionnelle 16c se traduit, après franchissement de la lame à retard quart d’onde 16d, par l’émission, par la zone émettrice élémentaire correspondante, ici de la lame à retard quart d’onde 16d, d’une lumière ayant une polarisation linéaire avec un axe de polarisation dont l’orientation Os(z, j), dans le plan de la surface émettrice 16s, varie en fonction du déphasage j) induit par la cellule à cristaux liquides 16c(i,j), et donc varie en fonction de la commande appliquée à la cellule à cristaux liquides 16c(i,j). Dans un système de ce deuxième type, et d’après ce qui a été expliqué ci- . As above concerning the control of the liquid crystal cells 16c(i,j), it is understood that, depending on the control applied to the electrodes of a given liquid crystal cell 16c(i,j), it is possible to vary, and therefore control, the orientation 0s( i. / ) of the principal polarization axis of the polarized light emitted by the corresponding elementary emitting area 16s(i,j), in particular from an initial value, corresponding to the case where no voltage is applied to the electrodes of the liquid crystal cell 16c(i,j), and up to a final value, corresponding to a maximum voltage applied to the electrodes of the liquid crystal cell 16c(i,j).

[0124] The system in Figure 3 is an example of a system 10 according to a third type which belongs to the second family of embodiments implementing more particularly, as a variation of the polarization property of interest emitted, a controlled variation of the phase shift (p^ 6s(i,J) between the two orthogonal components of the electric field vector of the emitted polarized light. In systems of the third type, the emitting surface 16s is the surface of the two-dimensional matrix 16c of liquid crystal cells, and each elementary emitting zone 16s(i,j) is therefore directly determined by an associated liquid crystal cell 16c(i,j). Thus, for embodiments of this third type, but belonging to the second family of embodiments, the phase shift qA6c(L j) between the two orthogonal components of the electric field vector induced by a liquid crystal cell 16c(i,j) corresponds directly to the phase shift J) between the two orthogonal components of the electric field vector of the emitted polarized light, with therefore (p\ 6s( i, j ) = (p 16c ( i,j) • Such a system will, for example, be advantageously implemented in the case where the two-dimensional matrix 16c liquid crystal cell technology generates, as a function of the control applied to the liquid crystal cell 16c(i,j), a comparatively larger variation in the phase shift ¢165(i,j) = <p 16c(i, j) entre les deux composantes orthogonales du vecteur de champ électrique de la lumière issue de la cellule à cristaux liquides 16c(i,j) et donc émise par la zone émettrice élémentaire (par exemple avec l’utilisation de cellules à cristaux liquides de type « ECB »). Dans un tel cas, la propriété de polarisation d’intérêt émise sera donc le déphasage , ¢716s(i, j) = (p 16dj, j) between the two orthogonal components of the electric field vector of the light emanating from the liquid crystal cell 16c(i,j) and thus emitted by the elementary emitting zone. Therefore, the control means 100 of the two-dimensional matrix 16c of liquid crystal cells will be able to configure the latter such that the polarized light emanating from each of the liquid crystal cells 16c(i,j), and thus from each elementary emitting zone 16s(i,j), exhibits an elliptical polarization having, for each liquid crystal cell 16c(i,j) and therefore for each elementary emitting zone 16s(i,j), a phase shift ^16^( i, j) = tpl6c(A j) ordered between the two orthogonal components of the electric field vector of the light from the liquid crystal cell 16c(i,j) and therefore emitted by the elementary emitting zone, which follows a variation, in particular a triangular variation, as a function of the position of the elementary emitting zone 16s(i,j) along the primary direction Dl.

[0125] A fourth type of embodiment takes the form of systems that are analogous to those of the first type of embodiment, but which belong to the second family of embodiments, implementing more particularly, as a variation of the polarization property of interest emitted, a controlled variation of the phase shift 46.5(4j) between the two orthogonal components of the electric field vector of the emitted polarized light. Such systems will, for example, be advantageously implemented in the case where the technology of the two-dimensional 16c matrix of liquid crystal cells generates, as a function of the applied to the 16c(i,j) liquid crystal cell, a variation of the phase shift <pl6s(i, j) commandé entre les deux composantes orthogonales du vecteur de champ électrique de la lumière émise polarisée qui est comparativement plus importante (par exemple avec l’utilisation de cellules à cristaux liquides de type « ECB »).In this fourth type, the polarization property of interest emitted is therefore directly the phase shift ¢^16.544 j) between the two orthogonal components of the electric field vector of the light coming from the liquid crystal cell 16c(i,j) and therefore emitted by the elementary emitting area.Thus, the control means 100 of the two-dimensional matrix 16c of liquid crystal cells will be able to configure the latter such that the polarized light emanating from each of the liquid crystal cells 16c(i,j), and therefore from each elementary emitting zone 16s(i,j), exhibits an elliptical polarization having, for each liquid crystal cell 16c(i,j) and therefore for each elementary emitting zone 16s(i,j), a phase shift (pl65( i, j) = <p!6c(i, / ) entre les deux composantes orthogonales du vecteur de champ électrique de la lumière émise polarisée de la lumière issue de la cellule à cristaux liquides 16c(i,j) et donc émise par la zone émettrice élémentaire, qui suit une variation, notamment une variation triangulaire, en fonction de la position de la zone émettrice élémentaire 16s(i,j) selon la direction primaire Dl. .

[0126] In all the systems described above 10, belonging to the four types, and according to what has been explained above concerning the control of the liquid crystal cells 16c(i,j), it is understood that, depending on the control applied to the electrodes of a given liquid crystal cell 16c(i,j), it is possible to vary, and therefore to control, the orientation 0s(f, / ) of the main polarization axis and / or the phase shift (p 165(4 j) between the two orthogonal components of the electric field vector of the polarized light emitted by the corresponding elementary emitting area 16s(i,j), in particular from an initial value, for example a zero value, corresponding to the case where no voltage is applied to the electrodes of the liquid crystal cell 16c(i,j), and up to a final value, corresponding to a maximum voltage applied to the electrodes of the liquid crystal cell 16c(i,j).

[0127] Similarly, it is understood that the variation of the orientation θs(i, j) of the principal polarization axis and / or the phase shift θs(i, j) between the two orthogonal components of the electric field vector of the polarized light emitted by the elementary emitting zone is a continuous function of the voltage control applied to the electrodes of the associated 16c(i,j) liquid crystal cell. On the other hand, as seen above, the variation of the orientation θs(i, j) of the principal polarization axis and / or the phase shift θs(i, j) between the two orthogonal components of the electric field vector of the light emitted by the elementary emitting zone 16s(i,j) is not necessarily a linear or affine function of the voltage control applied to the electrodes of the associated 16c(i,j) liquid crystal cell, but this can be taken into account in a preliminary calibration procedure.

[0128] Such a preliminary calibration procedure may include, in particular, acquiring, for example with a digital polarimetric camera, possibly with the interposition of a quarter-wave delay plate, a series of calibration images of the emitting surface 16s. For each calibration image in the calibration series, the illumination device 16 can be controlled by applying, for each calibration image, a known predetermined control voltage to the electrodes of each liquid crystal cell 16c(i,j) of the two-dimensional matrix 16c. For example, for each image in the series, the illumination device 16 can be controlled by applying, for each calibration image, the same known predetermined control voltage to the electrodes of each liquid crystal cell 16c(i,j) of the two-dimensional matrix 16c.Between each calibration image, the predetermined control voltage known at the electrodes of each liquid crystal cell 16c(i,j) of the two-dimensional matrix 16c is varied in increments between a minimum and a maximum value. For each calibration image, a polarization property value received by the camera is recorded for each elementary emitting area 16s(i,j), which allows, possibly taking into account known elements in the path of the light, for example the presence of a quarter-wave delay plate 34 in the case of [Fig.3], the value of the polarization property of interest emitted (orientation of the principal polarization axis and / or phase shift) to be determined as a function of the applied voltage in order to determine, for each . elementary emitting area 16s(i,j), a calibration relationship between the voltage applied to the electrodes of the liquid crystal cell 16c(i,j) and the value of the polarization property of interest emitted from this elementary emitting area 16s(i,j), as received by the camera sensor.

[0129] In all embodiments, particularly those belonging to the first family, the orientation 0s(i,j) of the principal polarization axis of the light emitted by the elementary emitting zone can be specified relative to a reference orientation. The reference orientation for defining the orientation 0s(Z,j) of the principal polarization axis of the light emitted by the elementary emitting zone 16s(i,j) will, for example, by definition be the orientation of the principal polarization axis when no voltage is applied to the electrodes of the liquid crystal cell.It appears that, according to the characteristics of the two-dimensional 16c liquid crystal cell matrix, the final orientation value 0s(i,j) of the main polarization axis, corresponding to the maximum voltage applied to the electrodes of the 16c(i,j) liquid crystal cell, can reach, with respect to the reference orientation, an angle of at least 45 degrees, preferably of at least 70 degrees, and even more preferably of at least 90 degrees.

[0130] In all embodiments, as in the example in [Fig. 6], the triangular variation of the emitted polarization property of interest P(D1) is such that each primary period T1 is divided into only two parts: an increasing part T1c and a decreasing part T1d. In the increasing part, the emitted polarization property of interest P(D1) is a linearly increasing function of the position of the elementary emitting zone along the primary direction D1, and, over this increasing part, the emitted polarization property of interest P(D1) increases from a lower primary value P1min to an upper primary value Plmax.In the decreasing part, the polarization property of interest emitted P(D1) is a linear decreasing function of the position of the elementary emitting zone along the primary direction Dl, the polarization property of interest emitted P(D1) decreases from the upper primary value Plmax, to the lower primary value P1min.

[0131] In all cases, the triangular variation of the polarization property of interest emitted which is obtained on the emitting surface 16s is therefore a function which is continuous, which is periodic with respect to a primary period Tl along the primary direction Dl of the emitting surface 16s, and which, on each period Tl, consists of two successive linear parts Tic and Tld.

[0132] It will be seen that such a 16s emitting surface configuration allows, within the framework of an adapted process, the detection of refractive defects at all points of an inspected area with homogeneous sensitivity over the entire inspected area, and with high sensitivity.

[0133] Preferably, the increasing part Tic and the decreasing part Tld of each primary period Tl are of equal extent along the primary direction Dl. In other words, the slope of variation of the increasing linear function and the slope of variation of the decreasing linear function are preferably equal.

[0134] It should be noted that the linear and continuous nature of the triangular variation over each half-period must be considered in light of the necessarily discontinuous nature of the illumination device 16. Indeed, the triangular variation is obtained by differentiated control of the liquid crystal cells of the two-dimensional matrix 16c. The cells necessarily have an extent along the primary direction D1, so each elementary emitting area also has a corresponding extent over which the polarization property of interest emitted is constant. However, given the precision required for the method, it is possible to have a two-dimensional matrix 16c of liquid crystal cells configured so that, as seen from the camera sensor, the variation appears continuous and linear over each increasing and decreasing portion of each period.

[0135] Preferably, for the acquisition of a given primary partial image in the method (which will be explained further below), the illumination device 16 is controlled such that the polarization property of interest emitted from the light emitted by the elementary emitting zones follows said triangular variation as a function of the position of the elementary emitting zone along the primary direction D1, but is constant along a direction D2 perpendicular to the primary direction D1. Thus, the polarization property of interest emitted varies along a single direction D1 of the emitting surface and is constant along the perpendicular direction D2.

[0136] In preferred embodiments, the digital camera is a polarimetric digital camera 18, the system in this case being able to comprise a single digital camera.

[0137] Polarimetric cameras are known in particular, in which the polarimetric camera comprises a two-dimensional photoelectric sensor 22, the principle of which is illustrated in Figures 7 and 8. The photoelectric sensor 22 comprises photoelectric elements 26(n,k), each comprising a photoelectric cell 28(n,k) in front of which is arranged an individual linear analyzer 30(n,k) associated with the photoelectric cell 28(n,k) of this photoelectric element 26(n,k). The photoelectric sensor 22 comprises N distinct groups of four contiguous photoelectric elements, the individual linear analyzers 30(n,k) of which each have a polarization axis Ak. The four polarization axes Ak of ​​a given group of four photoelectric elements form two pairs (A1, A2) and (A3, A4) of orthogonal polarization axes, the two pairs being offset from each other by 45 degrees. angle.The notation used in this text identifies a 26(n,k) photoelectric element, or a photocell. The photoelectric element 28(n,k) or an individual polarization analyzer 30(n,k) is identified by the index doublet (n,k). The index n (ranging from 1 to N) identifies the group 26(n) to which it belongs, and the index k (ranging from 1 to 4) identifies its position within the group. The index k thus indicates the orientation of the polarization axis Ak of ​​the individual polarization analyzer 30(n,k) of this photoelectric element 26(n,k). The photoelectric sensor 22 of [Fig. 7] thus defines four families of photoelectric elements 26(n,k) which correspond to four distinct polarization analysis characteristics, those determined by the individual polarizing filters 30(n,k).Thus, the four distinct polarization analysis characteristics are four linear analyses along the four distinct polarization axes, e.g. two pairs (A1, A2) and (A3, A4) of orthogonal polarization axes, the two pairs being offset from each other by 45 degrees of angle, in one direction or the other.

[0138] In the examples described below, the following conventions have been adopted: - the Al polarization axis of the individual polarizing filters 30(n,l) is parallel to the AO polarization axis of the upstream linear polarizer 16b; - the A2 polarization axis of the individual polarizing filters 30(n,2) is offset by 90 degrees of angle with respect to the Al axis; - the A3 polarization axis of the individual polarizing filters 30(n,3) is offset by 45 degrees of angle in a given direction with respect to the Al axis; - the A4 polarization axis of the individual polarizing filters 30(n,4) is offset by 135 degrees of angle in the same direction given with respect to the Al axis.

[0139] Such a polarimetric camera 18, through its photoelectric sensor 22, therefore delivers a digital image, called the master image IM, which can contain as many pixels, called master pixels Pm(n,k), as the number 4xN of photoelectric elements. In such a master image IM, groups of pixels can be defined, each group of pixels being hereafter a composite pixel Pc(n), where each composite pixel Pc(n) groups the master pixels Pm(n,k) that correspond to a given group 26(n) of contiguous photoelectric elements, as defined above. Thus, to each distinct group 26(n) of contiguous photoelectric elements corresponds a composite pixel Pc(n) in the master image delivered by the photoelectric sensor 22. A composite pixel Pc(n) therefore comprises 4 master pixels Pm(n,k).A composite pixel Pc(n) can be considered as the image of an elementary area of ​​the imaged field, therefore in particular, an elementary area of ​​the container 12 which was at the inspection location 13 at the time of the acquisition of the master image IM. .

[0140] Furthermore, as illustrated more particularly in [Fig. 9], the master digital image IM can also be considered to comprise the number K of distinct partial digital images IPk (with k an integer ranging from 1 to K), each having N Partial pixels Ppk(n). The partial pixels Ppk(n) of each partial digital image IPk correspond, for a given partial digital image IPk, to the photoelectric elements 26(n,k) of the sensor 22, whose individual linear analyzer 30(n,k) has the same polarization axis. In other words, all the partial pixels Ppk(n) of a given partial image IPk are acquired through individual linear analyzers Ppk(n) that have a common polarization axis Ak for the partial digital image IPk. Note that each partial pixel of a partial digital image IPk is taken from one of the N composite pixels of the master digital image IM from which the partial digital image IPk is extracted. A partial pixel Ppk(n) of a partial image IPk is therefore a master pixel Pm(n,k) of the master image IM acquired by the polarimetric camera 18.

[0141] Advantageously, the partial images IPk are pixel-by-pixel superimposable. Indeed, for a given elementary area of ​​the container 12, it is known that the different master pixels Pm(n,k) of the composite pixel Pc(n) corresponding to the given elementary area are distributed, in the form of partial pixels Ppk(n), in each partial image IPk, with a single master pixel Pm(n,k) of the composite pixel Pc(n), in the form of a partial pixel Ppk(n), in each partial image IPk. It is understood here that, at the scale of the resolution of the master image IM, there is a shift between two partial images IPk, a shift which is known as a function of the known shift between the photoelectric elements 26(n,k) within a group 26(n).On the other hand, at the scale of the resolution of the partial IPk images, the partial IPk images can be considered as perfectly and directly superimposable, because two partial pixels Ppk(n) extracted from the same composite pixel will be images, albeit partial, of the same elementary area of ​​the imaged field, therefore of the container 12.

[0142] For example, the XCG-CP series polarimetric cameras marketed by Sony Group companies operate according to this principle. The same Sony Group companies market two-dimensional photoelectric sensors that incorporate a system of individual linear polarizing filters, each associated with a photoelectric cell according to the principle described above. These sensors, known by the references IMX250MZR / MYR, IMX253MAR / MYR, or IMX264MZR / MYR, are of CMOS technology and include individual linear polarizing filters formed directly on the component. A system will be described in more detail below in an embodiment implementing such a camera. Other camera manufacturers that could be implemented within the scope of the invention include Lucid Vision Labs, Inc., 130-13200 Delf Place, Richmond, BC, Canada, V6V 2A2.

[0143] The use of such a camera makes it possible to obtain, in a single acquisition, a series of several images of the same inspected area, qualified in the image sequence Partial images, in which each partial image contains an image of the inspected area but receives light through a linear polarization analyzer whose polarization axis has its own orientation. With a digital polarimetric camera as described above, the resulting partial images are necessarily acquired along the same optical axis. Furthermore, the resulting partial images are directly superimposable, such that each elementary area of ​​the inspected container is imaged by a corresponding partial pixel in each of the digital partial images in the series, thus eliminating the need for computationally intensive registration operations.

[0144] In other embodiments, conventional matrix digital cameras may be used, comprising a two-dimensional photoelectric sensor, monochrome or color, but insensitive to the polarization of light. In such embodiments, as illustrated in [Fig. 4], a set of several cameras will be used, for example, a set of two digital cameras 18.1, 18.2, each of which will then be associated with its own linear polarization analyzer 30.1, 30.2, the polarization axes A1, A2 of the two linear polarization analyzers 30.1, 30.2 being different from each other, preferably orthogonal to each other. In such cases, the digital image delivered by each of the two digital cameras 18.1, 18.2 will be called a partial digital image.

[0145] In the example of [Fig. 4], a semi-reflective blade 36 is positioned perpendicular to the optical axis of the first 18.1 of the two digital cameras. This allows some of the light emerging from the container 12 to be reflected back to the second 18.2 of the two digital cameras. The use of such a semi-reflective blade 36, with fine adjustment of the position of the two digital cameras, ensures that the container is observed along the same optical axis, at least in the area of ​​the inspection location 13. Thus, although the two digital cameras 18.1 and 18.2 are not positioned in the same location, the digital images they acquire are directly superimposable, without the need for computationally intensive registration operations.

[0146] However, it could quite easily be envisaged that the set of several digital cameras 18.1, 18.2 could be arranged side by side to observe the inspection location 13, and therefore the container 12, along two distinct optical axes. In such a case, the digital images acquired by the set of several digital cameras will need to be computer-registered in order to be superimposed. The registration matrix can, for example, be obtained as part of a preliminary calibration operation. Such a system comprising a set of several digital cameras, for example two digital cameras, with optical axes that are not coincident in the The inspection location area 13 can be used, in particular, when the illumination device is controlled in such a way that the emitted polarization property of interest varies along a single direction DI of the emitting surface and is constant along the perpendicular direction D2. In this case, it will be advantageous for the optical axes of the cameras in the set of several digital cameras to define a plane that contains the direction perpendicular to the primary direction D1, and therefore contains the direction D2 along which the emitted polarization property of interest is constant.

[0147] The examples illustrate the case in which the digital camera(s) 18, 18.1, 18.2 are oriented so as to be perpendicular to the wall of the container 12 to be inspected. However, it is entirely possible to provide that the optical axis of the camera(s) 18, 18.1, 18.2 observe the container 12 at a certain downward or downward angle relative to the principal axis A12 of the container 12, for example as illustrated in [Fig. 11]. Preferably, the optical axis of the digital camera(s) 18, 18.1, 18.2 forms an angle greater than 45°, preferably greater than 60°, with the principal axis A12 of the container 12.

[0148] It is also noted that some of the systems 10, in particular the systems 10 belonging to the second or third type, include, in the path of the light between the two-dimensional matrix 16c of liquid crystal cells and the linear analyzers 30(n,k), 30.1, 30.2, a quarter-wave delay plate 16d, 34. Preferably, this quarter-wave delay plate 16d, 34 has a fast axis oriented parallel or perpendicular to the polarization axis A0 of the upstream linear polarizer 16b.

[0149] The presence of such a quarter-wave delay plate 16d, 34 makes it possible to recover, at the level of the polarimetric camera 18 or at the level of the linear analyzers 30.1, 30.2 of the conventional digital cameras 18.1, 18.2, an elliptically polarized light (in some cases linearly) whose principal polarization axis has an orientation which varies according to the control setpoint applied to the corresponding liquid crystal cell 16c(i,j) belonging to the two-dimensional matrix 16c.

[0150] However, as can be seen for the systems 10 belonging to the first family, the presence of such a quarter-wave delay plate is not mandatory, as shown, for example, by the embodiments in Figures 1, 4, and 5. In such a case, elliptically polarized light is recovered at the level of the polarimetric camera 18 or at the level of the linear analyzers 30.1, 30.2 of conventional digital cameras 18.1, with the orientation 0s ( ù j ) of the principal polarization axis of the emitted polarized light varying according to the control applied to the corresponding liquid crystal cell 16c(i,j) belonging to the two-dimensional matrix. sionnelle 16c.

[0151] In the presence of a quarter-wave delay plate in the path of the light, the latter can occupy one or the other of the following preferred positions.

[0152] In the second embodiment of Figure 2, the quarter-wave delay plate 16d is part of the illumination device 16 and is arranged in the path of the light between the two-dimensional array 16c of liquid crystal cells and the inspection location 13 where the container 12 to be inspected is to be placed. In this case, the incident light illuminating the container 12 is linearly polarized light whose polarization axis has an orientation ôs(z, j) that varies according to the control applied to the corresponding liquid crystal cell 16c(i,j) belonging to the two-dimensional array 16c.

[0153] In the third embodiment of Figure 3, the quarter-wave delay plate 34 is arranged in the path of the light between, on the one hand, the inspection location 13 where the container 12 to be inspected is to be placed, and, on the other hand, the linear analyzers 30(n,k), 30.1, 30.2 respectively of the polarimetric camera 18 or the conventional digital cameras 18.1, 18.2, therefore downstream of the container 12 to be inspected. In this case, it is observed that the incident light illuminating the container 12 is elliptically polarized light, with a phase shift q>I6s(i, j) between the two orthogonal components of the electric field vector which varies according to the control applied to the corresponding liquid crystal cell 16c(i,j) belonging to the two-dimensional matrix 16c.It is noted that, as schematically represented in the drawings, the arrangement of the quarter-wave delay blade downstream of the container 12 can allow the use of a quarter-wave delay blade 34 of smaller dimensions than the corresponding dimensions of the area to be inspected of the container, in any case when the digital camera(s) have a conventional lens with a diverging field of view, therefore not telecentric. In these embodiments, the quarter-wave delay plate 34 is interposed between the container 12 and the photoelectric elements 26(n,k) of the photoelectric sensor 22. The quarter-wave delay plate 34 interposed in the path of the light downstream of the inspection location 13 can be part of the polarimetric camera 18, either by being integrated into the photoelectric sensor 22, or by being placed between the lens 24 and the photoelectric sensor 22, or by being integrated into the lens 24. However, as in the example illustrated in [Fig.3], the quarter-wave delay plate 34 can be placed between the inspection location 13 of the system 10, to which the container 12 must be placed for inspection, and the objective 24 of the polarimetric camera 18. In an example not shown, but which would be of the third type while comprising, in a manner comparable to the example in [Fig. 4], two conventional digital cameras, the quarter-wave delay plate 34 would be placed between the inspection location 13 of the . system 10, to which the container 12 must be placed for inspection, and the respective linear analyzers 30.1, 30.2 of the conventional digital cameras 18.1, 18.2. In such an example, two quarter-wave delay plates 34 could be provided, each of which would be placed downstream of the semi-reflective plate 36, but alternatively, a single quarter-wave delay plate 34 could be provided between the inspection location 13 of the system 10, to which the container 12 must be placed for inspection, and the semi-reflective plate 36.

[0154] The systems 10 described above are examples of systems that each allow the implementation of at least some variants of an opto-computer process for through-light inspection of a glass container using a digital camera, as described below. The process includes computer steps, in particular computer calculation steps that can, for example, be performed by the computing unit 110. In system 10, the computing unit 110 can thus be programmed to perform all or part of the process or processes described below.

[0155] The methods described below are opto-computer methods for through-light inspection of a glass container moving along a trajectory. These methods are therefore implemented to inspect a glass container when it is brought to the inspection location 13 of the system 10.

[0156] The main steps of an example of the realization of such a process are described below with reference to the diagram in [Fig. 10].

[0157] The method includes illuminating the container 12 by an illumination device, for example by an illumination device 16 as described above.

[0158] The method includes observation 1020 of the container by at least one digital camera. Depending on the systems 10 implemented, it has been seen that there could be a single polarimetric camera 18, or a set of several conventional digital cameras, in particular two conventional digital cameras 18.1, 18.2, each equipped with a corresponding linear polarization analyzer 30.1, 30.2. In all cases, the digital camera(s) 18, 18.1, 18.2 each include a two-dimensional photoelectric sensor comprising photoelectric elements, each of which includes a photoelectric cell corresponding to a pixel in an image acquired by the digital camera. Since this is a through-light inspection, at least one digital camera 18, 18.1, 18.2 is located, with respect to the displacement path T, on the opposite side to that of the illumination device 16, so as to collect, by at least one digital camera 18, 18.1, 18.2 an emergent light emanating from the container 12 located at the inspection location 13. .

[0159] The method comprises the acquisition 1030, with at least one camera 18, 18.1, 18.2, of digital images which will hereinafter be referred to as partial digital images IPk. More precisely, this acquisition involves acquiring, for a given container, at least one series Sm (m being an integer identifying the series Sm) comprising, for at least a first series SI, at least one first partial digital image IP1.1 and a second partial digital image IP2.1. Each partial digital image IPk.m of a given series Sm for a given container contains an image of the same inspected area of ​​the container. Each partial digital image IPk.m comprises N partial pixels, each of which is the image of a corresponding elementary area of ​​the container. Each partial digital image IPk.m is acquired with the interposition, between the container 12 and the photoelectric cells of at least one camera 18, 18.1, 18.2 that acquires this partial digital image, of a linear analyzer having a given polarization axis Ak for a given partial digital image. For the acquisition of the first partial digital image IP1.m and the second partial digital image IP2.m of the same series Sm for a given container 12, the polarization axes A1, A2 of the implemented linear analyzers are distinct from each other, preferably orthogonal to each other.

[0160] In embodiments comprising a set of several conventional digital cameras 18.1 and 18.2, such as the embodiment illustrated in [Fig. 4], each of the cameras in the set of several conventional digital cameras acquires a partial digital image, respectively through the linear polarization analyzer 30.1, 30.2 associated with it. Thus, in the case of a set of several cameras comprising at least two conventional digital cameras 18.1 and 18.2, a first conventional digital camera 18.1 acquires, for a given container and for a given series Sm for that container, a first partial image IP1.m, through a first linear polarization analyzer 30.1 having a first polarization axis A1, and a second conventional digital camera 18.2 acquire, for the same given container and for the same given series for this container, a second partial image IP2.m, through a second linear polarization analyzer 30.2 having a second polarization axis A2 different from the first polarization axis, preferably orthogonal to the first polarization axis.

[0161] In embodiments that implement a polarimetric camera 18, the acquisition of a series Sm comprising at least one first partial digital image IP1.m and at least one second partial digital image IP2.m can be carried out in a single acquisition with the acquisition of a master image IM.m delivered by the polarimetric camera 18, the master image IM.m comprising, as seen above, four partial digital images IPk.m, the four partial digital images IPk.m each corresponding to a common polarization axis Ak for the individual linear analyzers 30(n,k) through which the partial pixels PPk.m(n) of the considered partial digital image IPk.n are acquired. For a series Sm . Given, the first partial digital image IP1.m and the second partial digital image IP2.m will therefore be chosen from among the four partial digital images IPk.m delivered by the polarimetric digital camera 18, preferably by choosing a pair of images corresponding to two polarization axes (A1, A2), (A3, A4) orthogonal to each other.

[0162] In all cases, the partial digital images IPk.m of the same series Sm are superimposable such that each elementary area of ​​the inspected area of ​​the container 12 is imaged by a corresponding partial pixel Ppk.m in each of the partial digital images IPk.m of the series Sm.

[0163] As indicated above, acquisition 1030 provides for the acquisition, for a given container, of at least one series Sm of partial digital images IPk.m, and therefore of at least one primary series SI of partial digital images IPk.l

[0164] For the primary series SI, the partial digital images IPk.l of the primary series SI each contain, in the background, the image of the same primary inspection portion of the emitting surface 16s. It is noted here that any light scattering through the container is assumed to be negligible; the container is therefore considered transparent. The primary inspection portion is observed through the container 12 by the digital camera(s). The primary inspection portion is thus the portion of the emitting surface that is seen, at the time of acquisition of the primary series SI of primary partial digital images IPk.l, through the inspected area of ​​the container 12 by the digital camera(s).For the acquisition of the primary SI series, the illumination device 16 is controlled so that, on the primary inspection portion of the emitting surface, the periodic variation law of the emitted polarization property of interest exhibits, along a primary direction DI of the emitting surface, a primary periodic variation, and displays several primary periods Tl over the extent of the primary inspection portion along the primary direction DI. More precisely, for the acquisition of the primary SI series of partial digital images IPk.l, the polarization property of interest emitted from the lights emitted by the elementary emitting zones of the primary inspection portion of the emitting surface 16s follows, over a primary period Tl, a triangular variation as a function of the position of the elementary emitting zone along the primary direction Dl, this triangular variation exhibiting several successive primary periods Tl, each of which exhibits such a triangular variation of the polarization property of interest emitted as a function of the position of the elementary emitting zone along the primary direction DL.

[0165] Preferably, for a given container 12, the partial digital images IPk.m of the same series Sm are acquired at the same instant. This simultaneity of the acquisition of the partial digital images IPk.m of the same series Sm is indeed This is understood to be obtained intrinsically when a polarimetric digital camera 18 is used for acquisition. In the case of a system implementing a set of several conventional digital cameras 18.1, 18.2, the control means 100 of the system 10 will be programmed so that the cameras in the set of several conventional digital cameras 18.1, 18.2 are synchronized in order to perform their respective acquisitions at the same instant. This simultaneous acquisition eliminates the risk of movement of the container 12 that would exist if the partial digital images of the same series were acquired at different times.

[0166] In certain embodiments, particularly those employing a polarimetric camera 18 as defined above, for the same inspected area of ​​the same container 12, it may be possible to acquire, for a given series Sm, for example the primary series SI, a third partial digital image IP3.1 and a fourth partial digital image IP4.1 for which the polarization axes A3, A4 of the linear analyzers are distinct from each other and distinct from the polarization axes A1, A2 of the linear analyzers for the first partial digital image IP1.1 and the second partial digital image IP2.1 of the series, preferably orthogonal to each other and offset by 45 degrees from the polarization axes A1, A2 of the linear analyzers for the first partial digital image IP1.1 and the second partial digital image IP2.1 of the SI series. It will be seen that the acquisition of a third partial digital image IP3.1 and a fourth partial digital image IP4.1 allows for better homogeneity in the calculation of the raw refraction image, which will be described below.

[0167] Indeed, after the acquisition of the partial digital images IPk.l for the primary series SI, the method includes the computer calculation 1040 of at least one raw primary refraction image IR1, from the partial digital images IPk.l of the primary series SI, by calculating, for each of the elementary zones of an inspected zone of the container, a raw primary refraction pixel Prl(n) whose value is representative of the refraction induced by the elementary zone of the inspected zone, from the value of the corresponding partial pixels Ppk.l(n) which are the image of the elementary zone in the partial digital images IPk.l of the primary series SI.

[0168] Indeed, in the example, the raw primary refracted pixel will have a value that depends on the value of the polarization property of interest emitted by the elementary emitting zone of the emitting surface that is seen, by the raw primary refracted pixel (more precisely by the given group 26(n) of contiguous photoelectric elements that deliver the corresponding partial pixels Ppk.l(n) which are the image of the elementary zone of the container), in the background through the corresponding elementary zone of the container. Now, which of the elementary emitting zones is thus seen depends on the refraction induced by the elementary zone of the inspected area. Indeed, by traversing, In the opposite direction of propagation, the path of light from a partial pixel to an elementary emitting zone of the emitting surface undergoes refraction at each interface crossing, and therefore at each surface of the glass wall of the container traversed. This light path thus depends on refraction. Therefore, the elementary emitting zone of the emitting surface connected by this light path to a partial pixel depends on the induced refraction. And, since distinct elementary zones do not have the same value of the polarization property of interest emitted, it follows that the raw refractive index (Prl(n)) of the primary pixel is representative of the refraction induced by the elementary zone of the inspected area.

[0169] Insofar as the polarization property of the lights emitted by the elementary emitting areas of the primary inspection portion of the emitting surface 16s follows a triangular variation as a function of the position of the elementary emitting area along the primary direction Dl, a raw primary refraction pixel Prl(n) will have a value that will be representative of the refraction induced by the elementary area of ​​the inspected area, in that it will be representative of the refraction along the primary direction Dl.

[0170] Refraction along a given direction, for example along the primary direction Dl, can be defined as the component, along the given direction, of the change in direction of propagation of light for light rays which pass through this elementary zone.

[0171] In a preferred example, Dl is parallel to the axis A12 of the inspected container. For a theoretical perfect container 12 whose body would be in the shape of a glass cylinder of constant thickness, the refraction of light rays from the emitting surface 16s and passing through the optical center of the lens 24 (i.e., the principal rays) is always the same, uniform, and predictable in the direction Dl. In the raw primary refraction image IR1, each raw primary refraction pixel Prl(n) theoretically has (in the absence of a refracting defect) an expected property value that corresponds to the polarization property of light emitted by an emitting area, and which therefore follows a triangular function of the position of each raw primary refraction pixel Prl(n) in the image along the direction Dl.If the raw primary refraction pixel Prl(n) belongs to the image of a defect producing a refraction anomaly of a given angle on the path of the light from the elementary zone of the inspected zone, the raw primary refraction pixel Prl(n) will have a value corresponding to the value of the polarization property of interest emitted from another elementary emitting zone 16s(i,j), therefore a different value from the expected one, and, as the triangular variation function is continuous and piecewise linear, the difference between the calculated value and the expected value is a function of the refraction anomaly, that is to say a function of the deviation of the light beams with respect to their propagation in . air or through a perfect container.

[0172] Depending on the system 10 implemented, but also depending on the number of partial digital images acquired for a given series, for the given container 12, different calculation algorithms can be implemented, which will be detailed below.

[0173] In such a raw primary refraction image IR1, it will be possible to detect anomalies induced by refractive defects in the inspected area of ​​the container. Indeed, in the raw primary refraction image IR1, a raw primary refraction pixel Prl(n) is calculated for each elementary zone of the inspected area of ​​the container. Now, for a given elementary zone of the container, the value of this raw primary refraction pixel Prl(n) necessarily depends on the value of the polarization property of interest emitted from the emitting elementary zone that is seen through the given elementary zone of the container.For two given elementary zones of the container that are close to each other but offset from each other along the primary direction Dl, two raw primary pixel values ​​were calculated: a value Prl(n) corresponding to the first elementary zone, and a value Prl(n') corresponding to the second elementary zone of the container. In the absence of any refractive anomaly induced by a defect refracting this zone of the container (or therefore in the absence of a container at inspection location 13), the variation between these two raw primary pixel values ​​would thus solely reflect the variation between the values ​​of the polarization property of interest emitted for the two corresponding emitting elementary zones of the emitting surface 16s, a variation which is known and is a triangular variation.In the presence of the container 12, the latter can, in the absence of any refracting defect, induce a certain refraction value. However, for two given elementary zones of the container that are close to each other and offset from each other along the primary direction Dl, it is expected that, in the absence of a refracting defect, the variation between the two corresponding raw primary pixel refraction values ​​Prl(n) and Prl(n') will be a linear variation reflecting the linear variation between the values ​​of the polarization property of interest emitted for the two corresponding emitting elementary zones.If this is not the case, and therefore if, for two given elementary zones of the container that are close to each other and offset from each other along the primary direction Dl, a sharp variation is observed between the two values ​​Prl(n) and Prl(n') of the corresponding raw primary refractive pixels, then we can conclude the presence of a refractive anomaly, which can be attributed to the presence of a refracting defect. Furthermore, the difference in values ​​between two raw primary refractive pixels Prl(n) and Prl(n') aligned in the direction Dl depends directly on the distance in the direction Dl between the two elementary zones of the inspected area that they see. each one in the background of the container.

[0174] It should be noted, however, that, starting from only the partial digital images acquired in the primary series SI, it will only be possible to detect refracting defects which induce a refraction with an angle of refraction in a plane containing the primary direction Dl.

[0175] In particular, in cases where the polarization property of interest emitted from the light emitted by the elementary emitting areas is constant along a direction perpendicular to the primary direction Dl, a refracting defect which would induce a refraction, with an angle of refraction contained in a plane perpendicular to the primary direction Dl, would not be detectable.

[0176] To be able to reliably detect refractive defects regardless of the orientation of the refraction they generate, it is therefore advantageous that, for the same inspected area of ​​the same container 12, the acquisition includes the acquisition of at least one secondary series S2 of partial digital images IPk.2 comprising at least one first partial digital image IPI.2 and a second partial digital image IP2.2.

[0177] In a strictly analogous manner to what has been seen for the primary series SI, it is foreseen that, for the secondary series S2, the partial digital images IPk.2 each contain, in the background, the image of the same secondary inspection portion of the emitting surface 16s, the secondary inspection portion being observed through the container 12 by the digital camera, and, on the secondary inspection portion of the emitting surface, the law of periodic variation of the polarization property of interest emitted exhibiting, along a secondary direction D2 of the emitting surface, different from the primary direction Dl, preferably orthogonal to the primary direction Dl, a secondary periodic variation, and exhibiting several secondary periods T2 over the extent of the secondary inspection portion along the secondary direction D2.Just as was defined for the variation of the polarization property of interest emitted along the primary direction D1, over a secondary period T2, the polarization property of interest emitted from the lights emitted by the elementary emitting zones of the secondary inspection portion of the emitting surface 16s preferably follows a triangular variation as a function of the position of the elementary emitting zone along the secondary direction D2. The secondary period T2 may be equal to, or different from, the primary period T1.

[0178] Preferably, the primary inspection portion of the emitting surface 16s and the secondary inspection portion of the emitting surface 16s are not coincident in both time and space.

[0179] In other words, the primary inspection portion of the emitting surface 16s and the secondary inspection portion of the emitting surface 16s can coincide in time, that is, to be activated at the same time, but not to be coincident in space. For example, the primary inspection portion and the secondary inspection portion of the emitting surface 16s may be distinct portions of the emitting surface 16s. In such a case, the illumination device 16 may comprise two distinct physical components or sets of physical components, for example, two distinct sets of physical components, each of them taking, for example, the form of the set of physical components described for the illumination device in the embodiments of Figures 1 to 5, with a first set of physical components comprising the primary inspection portion of the emitting surface 16s, and a second set of physical components comprising the secondary inspection portion of the emitting surface 16s, the emitting surface 16s being in this case distributed over the two sets of physical components.Alternatively, the primary inspection portion and the secondary inspection portion of the emitting surface 16s can be distinct portions of an emitting surface 16s formed by a single set of physical components as described for the illumination device in the embodiments of Figures 1 to 5. In this case where the primary inspection portion of the emitting surface 16s and the secondary inspection portion of the emitting surface 16s are not coincident in space, the method can include the acquisition, for the same inspected area of ​​the same container, of the primary series of partial digital images and the secondary series of partial digital images at the same time or at different times.In this case where the primary inspection portion of the emitting surface 16s and the secondary inspection portion of the emitting surface 16s are not coincident in space, the primary series of partial digital images and the secondary series of partial digital images can be acquired respectively with different cameras, possibly at different inspection locations along the path of the containers.

[0180] Conversely, the primary inspection portion of the emitting surface 16s and the secondary inspection portion of the emitting surface 16s may be coincident in space, or at least partially coincident in space, but not coincident in time, i.e., be activated at different times. This proves particularly possible with the implementation of a two-dimensional matrix 16c of liquid crystal cells, since by changing the control of the dimensional matrix 16c of liquid crystal cells, it is possible, at a first instant, to generate on a portion of the emitting surface 16s a variation of the polarization property of interest emitted only along the primary direction Dl, and, at a second instant different from the first instant, to generate, on the same portion of the emitting surface 16s, a variation of the same polarization property of interest emitted only along the Secondary direction D2. Thus, in this latter case, the primary inspection portion and the secondary inspection portion correspond to two different polarization states, at different times, of the same inspection portion of the emitting surface 16s. In this case, it is understood that what is considered the same inspection portion of the emitting surface 16s must, of course, cover the positions of the container at the two acquisition times, respectively of the primary and secondary series. If the article is in motion between the two acquisition times, the said same inspection portion of the emitting surface 16s must, of course, cover the positions of the container at these two times, although the article will not have exactly the same relative position with respect to the said same inspection portion.What matters here is that the same inspection portion, which is used for acquiring both the primary and secondary series, must change its polarization state, with respect to the polarization property of interest emitted, between the acquisition time of the primary series and the acquisition time of the secondary series. At the acquisition time of the primary series, the polarization property of the lights emitted by the elementary emitting zones of the inspection portion of the emitting surface 16s follows a triangular variation depending on the position of the elementary emitting zone along the primary direction D1. At the acquisition time of the secondary series, the polarization property of the lights emitted by the elementary emitting zones of the same inspection portion of the emitting surface 16s follows a triangular variation depending on the position of the elementary emitting zone along the secondary direction D2.In this case, where the primary inspection portion of the emitting surface 16s and the secondary inspection portion of the emitting surface 16s are spatially coincident, the acquisition, for the same inspected area of ​​the same container, of the primary series of partial digital images and the secondary series of partial digital images is carried out at different times. In this case, the primary series of partial digital images and the secondary series of partial digital images can be acquired with the same polarimetric camera 18 or with the same set of several conventional digital cameras 18.1, 18.2. Thus, a system 10 can be implemented in which the control of the two-dimensional array 16c of liquid crystal cells is synchronized with the acquisition, with at least one camera, i.e., with the same polarimetric camera 18 or with the same set of several conventional digital cameras 18.1, 18.2, of the at least two partial digital images necessary for the process, so as to: . - acquire a primary SI series of at least two partial digital images when the two-dimensional 16c array of liquid crystal cells is controlled such that the controlled polarization property of the light from a cell given 16c(i,j) liquid crystals, follows a triangular variation as a function of the position of the elementary emitting zone, associated with the given 16c(i,j) liquid crystal cell, along the primary direction Dl; - acquire a secondary series S2 of at least two partial digital images when the two-dimensional array 16c of liquid crystal cells is controlled such that the controlled polarization property of the light from a given 16c(i,j) liquid crystal cell follows a triangular variation as a function of the position of the elementary emitting area associated with the given 16c(i,j) liquid crystal cell, along a secondary direction D2 different from the primary direction Dl, preferably orthogonal to the primary direction Dl.

[0181] Thus, during the passage of a given container 12 to the inspection location 13, the method may include controlling the two-dimensional array 16c of liquid crystal cells such that, successively, for the acquisition of the primary series of partial digital images of the given container, the controlled polarization property of the light from a given liquid crystal cell 16c(i,j) follows a triangular variation as a function of the position of the given liquid crystal cell 16c(i,j) along the primary direction Dl, while being constant along a secondary direction D2 different from the primary direction Dl, preferably orthogonal to the primary direction Dl, and then such that, for the acquisition of the secondary series of partial digital images, this same controlled polarization property follows a triangular variation as a function of the position of the liquid crystal cell 16c(i,j) given along the secondary direction D2, while being constant along the primary direction D1.

[0182] In the case where the primary and secondary series are acquired at different times, the movement of the containers 12 can be interrupted between the two times such that, for both the primary and secondary series, the inspected container 12 is in exactly the same position. However, continuous movement of the containers is generally preferred. In the case of continuous movement of the containers, acquiring the primary and secondary series at different times necessarily implies that the inspected container 12 is in different positions for the two acquisitions.However, it can be expected that the acquisition frequency of currently available cameras, and the switching speed of the two-dimensional arrays 16c of liquid crystal cells, allow the displacement of a container 12 between the acquisition of the primary series and the acquisition of the secondary series to be small, the container 12 remaining, in the time interval defined by these two instants, between the illumination device 16 used and the same polarimetric camera 18 or the same set of several conventional digital cameras 18.1, 18.2. For example, the time interval between the 2 acquisitions. The acquisition time is 1 ms, while the containers move at a speed of Im / s, thus moving 1 mm between two acquisitions. If the time interval between the primary and secondary acquisitions increases, a shift in the inspection portion of the emitting surface in the direction of container movement, as explained previously, can be expected.

[0183] Just as for the variation, along the primary direction D1, of the emitted polarization property of interest, the triangular variation, along the secondary direction D2, of the emitted polarization property of interest is such that each secondary period is preferably divided into only two parts, an increasing part and a decreasing part.In the increasing portion, the emitted polarization property of interest is a linearly increasing function of the position of the elementary emitting zone along the secondary direction D2, increasing from a lower secondary value to an upper secondary value. In the decreasing portion, the emitted polarization property of interest is a linearly decreasing function of the position of the elementary emitting zone along the secondary direction D2, decreasing from the upper secondary value to the lower secondary value. Similarly, as with the variation of the emitted polarization property of interest along the primary direction D1, the increasing and decreasing portions of each secondary period are preferably of equal extent along the secondary direction D2.

[0184] With the acquisition of a secondary series of partial digital images as defined above, the method can therefore include the computer calculation of at least one raw secondary refraction image IR2, from the partial digital images IPk.2 of the secondary series S2, by calculating, for each of the elementary zones of the inspected zone of the container 12, a raw secondary refraction pixel Pr2(n), the value of which is representative of the refraction undergone by the light having passed through at least one wall thickness of the container 12 and emerging from the elementary zone, from the value of the corresponding partial pixels Ppk.2(n) which are the image of the elementary zone in the partial digital images IPk.2 of the secondary series S2.

[0185] Insofar as the polarization property of the lights emitted by the elementary emitting areas of the secondary inspection portion of the emitting surface 16s follows a triangular variation as a function of the position of the elementary emitting area along the secondary direction D2, a raw secondary refraction pixel Pr2(n) will have a value that will be representative of the refraction induced by the elementary area of ​​the inspected area, in that it will be representative of the refraction along the primary direction D2.

[0186] We will now describe different ways of computationally calculating a raw IRm refraction image from the partial digital images IPk.m of the Sm series corresponding, by calculating, for each of the elementary zones of an inspected zone of the container 12, a raw refraction pixel Prm(n) whose value is representative of the refraction induced by the elementary zone, from the value of the corresponding partial pixels Ppk.m(n) which are the image of the elementary zone in the partial digital images IPk.m of the corresponding series Sm.

[0187] For the mathematical formulas below, we preferably consider the case where the polarization axes A1 and A2, corresponding respectively to the first and second partial images of the series Sm under consideration, are orthogonal to each other. If, however, the mathematical formulas make use of the third partial image IP3.m and the fourth partial image IP4.m of a given series Sm, we consider the case where the polarization axes A3 and A4, corresponding respectively to the third partial image IP3.m and the fourth partial image IP4.The m of the series Sm considered, are orthogonal to each other, and oriented at 45° to the polarization axes Al and A2 corresponding respectively to the first partial image and the second partial image of the series Sm considered, are orthogonal to each other, thus with two pairs (Al, A2) and (A3, A4) of orthogonal polarization axes, the two pairs being offset from each other by an angle of 45 degrees.

[0188] We will first differentiate two categories of embodiments, depending on the nature of the polarization of the light received at the level of the polarimetric camera 18 or, where applicable, at the level of the linear analyzers 30.1, 30.2 of the conventional digital cameras 18.1, 18.2.

[0189] The process is first described for a first category of embodiments which includes the first, second and third types of embodiments. In the first type of embodiment, the polarization property of interest emitted is the orientation 0s(z, j) of the principal polarization axis of the emitted polarized light, which is then not modified by the system 10 between the emitting surface 16s and the polarimetric camera 18 or, where applicable, at the linear analyzers 30.1, 30.2 of conventional digital cameras 18.1, 18.2, except for modification induced by a container 12. In the second and third types of embodiments, the presence of a quarter-wave delay plate 16d, 34 in the path of the light makes it possible to recover, just as in the first type of embodiment, at the polarimetric camera 18 or, where applicable, at the linear analyzers 30.1, 30.2 of the conventional digital cameras 18.1, 18.2, an elliptically polarized light (in some cases linearly) whose principal axis of polarization has an orientation ar(n), which will be called hereafter the received polarization orientation ar(jï). The received polarization orientation ar(n) is determined for each elementary zone of the inspected zone of the container 12. In other words, in the particular case of the use of a polarimetric digital camera 18, . the received polarization orientation ar(n) is determined for each group of partial pixels which, in a municipal image acquired by a polarimetric camera, belong to the same composite pixel Pc(n).

[0190] The received polarization orientation ar(n) is determined by arbitrary reference to The orientation of the polarization axis corresponding to one of the partial digital images in the series, for example, the first partial digital image IPl.m. The received polarization orientation ar(n) is therefore the angular difference between the principal polarization axis of the elliptically polarized light received at the polarimetric camera 18 or, where applicable, at the linear analyzers 30.1, 30.2 of the conventional digital cameras 18.1, 18.2, and the polarization axis Al corresponding to the first partial digital image IPl.m. In the example developed, it is recalled that the first partial digital image IPl.m is an image whose partial pixels Ppl.m(n) are acquired through a polarization analyzer 30(1,n), 30.1 whose polarization axis Al is parallel to the polarization axis A0 of the upstream linear polarizer 16b of the illumination device 16.It is also recalled that, for the second and third type embodiments, a quarter-wave delay plate 16d, 34 is interposed in the path of the light with its fast axis which is also parallel to the axis A0 of the upstream linear polarizer 16b (but the same formulas also apply with a fast axis perpendicular to the axis A0, with only a reversal of the direction of rotation).

[0191] For this first category of embodiments, the calculation of the raw image of Refraction relies, for each raw refracted pixel Prm(n), on the Stokes parameters which, for any polarization, can be expressed according to the following relation, as a function of the received polarization orientation ar(n), the polarization ellipticity θ) and the degree of polarization p(n) of the light received at the polarimetric camera 18 or at the linear analyzers 30.1, 30.2 of conventional digital cameras 18.1, 18.2. This relation can be written:

[0192] [Math.l] '50' SI S2 ,S3. = pn co if €(n)cos2ar(ri) cos2e(n)sin2ar(n) sin2e(n)

[0193] Now, in a known manner, these same Stokes parameters can also be written, in terms of the intensity of the light received at the level of each photoelectric cell 28(k,n) corresponding to the elementary zone: ■50' SI S2 .S3.

[0194] [Math.2] PpLn^n) + Pp2jn(ny Pp\m(ïi) - Pp2m(n) Pp3jn(n) - Pp4.m(n) ylstf-Sl 2 -S2 2

[0195] From these two mathematical relationships, we can deduce a first formula for calculating a value of the received polarization orientation ar(n) from only the values ​​of two corresponding partial pixels Ppk.m(n) in the first partial image and the second partial image of the series Sm considered, this formula being able to be written:

[0196] [Math.3] JP pim (“) —TT

[0197] In cases where, for a given series Sm, there are 4 partial digital images corresponding to two pairs (A1, A2) and (A3, A4) of orthogonal polarization axes, the two pairs being offset from each other by an angle of 45 degrees, a value of the received polarization orientation ar(n) can be calculated from the arctangent of a ratio between, on the one hand, the difference in value of two corresponding partial pixels (Ppk.m(n)) in the first partial image and the second partial image, and, on the other hand, the difference in value of the two corresponding partial pixels (Ppk.m(n)) in the third partial image IP3.m and the fourth partial image IP4.m, for example by following the formula:

[0198] [Math.4] " _ 1 / PP3jn (n) \ 2 atan[ Ppljjt (nypp2.m (n^

[0199] In practice, this latter case, which is based on 4 partial digital images corresponding to two pairs (A1, A2) and (A3, A4) of orthogonal polarization axes, the two pairs being offset from each other by 45 degrees of angle, makes it possible to obtain a calculation of the received polarization orientation ar(n) which is less sensitive to noise and which therefore has the same sensitivity over the entire range of variation of the calculated value.

[0200] In this way, the triangular variation of the polarization property of the incident light emitted by the emitting surface 16c makes it possible to have, for the calculation of the value of the raw refraction pixel calculated, which value is representative of the refraction undergone by the light emerging from the elementary area, a sensitivity which is substantially equal over the extent of the inspected area.

[0201] In both cases, we can thus, for this first category of modes of rea In this process, define the raw IRm refraction image for the Sm series as a calculated digital image whose pixels Prm(n), each corresponding to an elementary zone of the container, are defined from the arctangent of a ratio between the values ​​of two corresponding partial pixels Ppk.m(n) in the first and second partial images of the considered Sm series, for example by following the formula:

[0202] [Math.5] Prm(n) - ar(n)

[0203] In a second category of embodiments, which includes the fourth type of embodiment, elliptically polarized light is recovered at the polarimetric camera 18 or at the linear analyzers 30.1, 30.2 of conventional digital cameras 18.1, with a phase shift cpr(n) between the two orthogonal components of the electric field vector, and with this phase shift (pr(n)) varying. This phase shift will hereafter be called the received polarization phase shift. <pr(n). le déphasage de polarisation reçu <pr(ri) est déterminé pour chaque zone élémentaire la inspectée du récipient 12. en d’autres termes, dans le cas particulier l’utilisation d’une caméra numérique polarimétrique 18, (pr(n) groupe pixels partiels qui, une image maitresse acquise par appartiennent au même pixel composite pc(n).

[0204] For this second category of embodiments, the calculation of the raw refracted image is based on the following equations:

[0205] [Math.6] ' Pp Lm(n) = I cos2 ( (pr(n) ) Pp3.m(ri) = 0.5 / Pp2.m(ii) = I cos2 ( <pr(n) + y ) ppa-m^i)="0.5"

[0206] From these mathematical relationships, a formula can be deduced for calculating a value of the received polarization phase shift. <pr(jp à partir de seulement les valeurs deux pixels partiels ppk.m(n) correspondants dans la première image partielle et deuxième série sm considérée, cette formule pouvant s’écrire selon l’une des formules ci-dessous :

[0207] [Math.7] (pi Ppim (n) Ppïm (n)

[0208] [Math. 8] / \ IPp3.m (n )-0.5 P p2m(n) ' y / y PpA-m ( / / )-0.5 PpLm(n)

[0209] Thus, for this second category of embodiments in which elliptically polarized light is recovered at the level of the polarimetric camera 18 or, where applicable, at the level of the linear analyzers 30.1, 30.2 of conventional digital cameras 18.1, 18.2, with a phase shift (pr(ri)) between the two orthogonal components of the electric field vector that varies, the raw IRm refraction image for the Sm series can be defined as a calculated digital image whose pixels Prm(n), each corresponding to an elementary zone of the container, are defined from the arctangent of a ratio between the values ​​of two corresponding partial pixels Ppk.m(n) in the first and second partial images of the Sm series under consideration, for example by following the formula:

[0210] [Math.9] Prm(n) = (praia)

[0211] In all cases, the raw IRm refraction image calculated using the methods and devices described above then allows, through refraction anomaly analysis, the detection of refractive defects in the glass constituting the bottle. The refraction anomaly analysis may also allow the detection of material distribution defects characterized by areas where the glass wall thickness varies significantly locally, leading to excessively thin wall sections. The refraction analysis step includes a computer calculation step based on the raw refraction image.

[0212] For example, the method may include a computer calculation step of the gradient in the raw primary refracted image along the primary direction D1, respectively in the raw secondary refracted image along the secondary direction D2. Alternatively, the raw refracted image may, for example, be analyzed by comparing it by computer calculation to a reference image.

[0213] For the analysis of refraction anomalies, one can for example calculate by computer, from the raw refraction image IRm, (resp. IR1, IR2), a refraction analysis image lARm (resp. IAR1, IAR2) composed of refraction analysis pixels Parm(n) (resp. Parl(n) Par2(n)) whose value represents the refraction, i.e. depends on the angles of deviation of the light rays deviated by the diopters made up of the glass wall surfaces crossed.

[0214] According to a first series of refraction analysis methods, based on a derivation, the refraction analysis image is obtained by applying to the raw refraction image IR1 (respectively IR2) a low-pass filter, or a gradient filter of the Sobel or Prewitt type, oriented in the direction of variation respectively Dl, respe tively D2. Since the difference in value between neighboring raw refraction pixels Prl(n) - Prl(n') (resp. Pr2(n) - Pr2(n')) is proportional to the deviation of the corresponding light rays passing through the container, then in the resulting refraction analysis image IAR1 (respectively IAR2), high values ​​of refraction analysis pixels Parl(n) (resp. Par2(n)) correspond to strong refractions, medium values ​​correspond to medium refractions, and low values ​​correspond to weak refractions. High refraction analysis pixel values ​​Par(n) (resp. Par2(n)) therefore correspond to refraction anomalies, i.e., refracting defects, for example, to locally very strong slope variations for the surfaces of the glass wall(s) corresponding to the high-value refraction pixels.

[0215] A second set of refraction analysis methods is based on a comparison with an expected reference variation, corresponding to a defect-free container. Theoretical refraction pixel values ​​Ptm(n), corresponding to a defect-free container, can be calculated, and a refraction analysis image can be obtained in which each refraction analysis pixel Parm(n) results from a pairwise comparison, for example by subtraction, of the raw refraction pixel Prm(n) with the corresponding theoretical refraction pixel value Ptm(n). Alternatively, the theoretical pixel values ​​Ptm(n) can be calculated by analyzing the raw refraction pixels Prm(n) in the direction D1 (respectively D2) to determine, by regression, an optimal triangular function.When the calculated raw refraction pixel values ​​do not correspond to the theoretical pixel values, the difference depends directly and proportionally on any refractive anomaly or deviation. In this case, the IAR1, IAR2 refraction analysis image can be analyzed not only by applying a computer-calculated derivation or gradient, to which a threshold is applied to detect refractive defects, but also by analyzing low spatial frequencies to determine regions of variation in glass distributions.

[0216] In this second series of refraction analysis methods, applied to a raw IR2 refraction image corresponding to a direction D2 perpendicular to the axis A12 of the container, it may be advantageous to take into account, in particular in the direction D2 (assumed here perpendicular to an axis of revolution symmetry A12 of the container 12), the predictable refraction from the circular shape of the section of cylindrical containers corresponding to the ideal model of a cylinder of constant thickness.

[0217] Other methods can be used to obtain the refraction analysis image, such as methods analogous to phase unfolding by computer calculation, as applied in deflectometry.

[0218] To obtain a given defect detection sensitivity, the following must be adapted: - the period of the variation function of the polarization property of interest emitted; - the resolution of the light source; - the resolution of the digital camera.

[0219] This means that it will be necessary to adapt both the resolution of the partial images delivered by the digital camera(s), but also to adapt the scale at which are seen, in the partial image, on the one hand a period, primary or secondary, of variation of the polarization property of interest emitted in the emitting surface and on the other hand a possible refracting defect in the material of the inspected area of ​​the container.

[0220] For this, it appeared optimal that a primary period T1, respectively secondary T2, of variation of the polarization property of interest emitted be seen by the two-dimensional photoelectric sensor 22 of the digital camera(s), with a resolution, according to the primary direction D1, respectively secondary D2, of at least 15 partial pixels, for example in the range from 15 to 500 partial pixels, of the same partial digital image.

[0221] Preferably, the inspected area of ​​the container 12 is seen by the two-dimensional photoelectric sensor 22 with a resolution, along the primary direction D1, respectively secondary D2, of at least 5 partial pixels of the same partial digital image per millimeter on the container.

[0222] To take into account the contrast effect of the variation in the polarization property of interest emitted on the refractive defects, the dimensioning of the periods is considered at the level of the inspected container 12, therefore, for example, at the level of its axis A12. Thus, by convention, as illustrated in Figures 11 and 12, a working plane W is defined containing the axis A13 of the inspection location 13 and orthogonal to a plane defined by the axis A13 and the optical axis of the digital camera, and one can then represent, as illustrated in Figures 11 and 12: - the periods T1 and T2 of variation of the variation function of the polarization property of interest emitted at the level of the emitting surface 16s along the directions respectively primary D1 and secondary D2, expressed in units of distance, for example in millimeters; - the reduced periods Tri and Tr2 corresponding respectively to the periods T1 and T2, in the working plane W containing the axis A13, by a homothety with center O, O being the optical center of the lens 24 of the digital camera 18, - the image periods Til and Ti2 of variation of the received polarization property, considered in the optical image, therefore in the image plane, therefore on the two-dimensional photoelectric sensor 22, according to the respective primary Dl and secondary D2 directions, expressed in number of pixels on the digital sensor 22.

[0223] Preferably, the image periods T1 and Ti2 of variation in the received polarization image IR1 and IR2 respectively, are between 15 and 500 pixels

[0224] For a camera resolution of 5 pixels per millimeter on the working plane W of the inspection location 13, and an image period Til and Ti2 of variation in the received polarization image IR1 respectively IR2 equal to 15 pixels, the reduced periods Tri and Tr2 are equal to 3 millimeters.

[0225] For a camera resolution of 10 pixels per millimeter on the working plane W of the inspection location 13, and an image period Til and Ti2 of variation in the received polarization image IR1 respectively IR2 equal to 500 pixels, the reduced periods Tri and Tr2 are equal to 50 millimeters.

[0226] In total, preferably, the reduced periods Tri and Tr2 are between 3 and 50 millimeters on the working plane W of the inspection location 13, the value being chosen in particular according to the size of the refractive defects that one wishes to be able to detect.

[0227] The resolution of the source is such that the polarization property of interest emitted by the 16s surface varies for each half-period Tic, Tld (respectively T2c, T2d) between a minimum value Plmin (resp. P2min) and a maximum value Plmax (resp. P2max), preferably passing through at least 16 increasing (respectively decreasing) intermediate values ​​Pmi in constant steps (or alternating between two different constant steps). When the setpoint of each cell is, for example, an 8-bit word, over the half-period Tic the setpoint varies, for example, from 0 for Plmin to 252 for Plmax in 64 steps of value 4.

[0228] The two-dimensional photoelectric sensor 22 and the lens 24 are, for example, chosen so that the resolution of each partial digital image is 5 pixels per millimeter on the plane W, therefore at least substantially 5 pixels per millimeter on the container 12. Thus the resolution of the raw MRI refraction images is at least substantially 5 raw refraction pixels per millimeter on the container 12.

[0229] The systems described above can advantageously be implemented to acquire, in addition to the images described above, at least one complementary master image IM' which will allow the calculation of a stress image of the inspected area and / or an intensity image for the inspected area, in order to assess the presence of residual mechanical stresses (stress) internal to the material of the container 12. More specifically, a stress defect generally consists of a foreign body creating internal mechanical stresses in the glass material, that these stresses make the material birefringent, and that this birefringence manifests itself by the polarization phase shift it induces in polarized light passing through this material. The stress image is a two-dimensional image calculated from a complementary master image IM', and in which Each pixel is a polarization phase-shift pixel Pd(n), that is, a measurement, as a polarization property of the light emerging from the container, of the phase shift between the two orthogonal components of the electric field vector of the light. For the acquisition of this complementary master image, the illumination device 16 is controlled such that the emitting surface 16s emits polarized incident light that is uniform in polarization over the entire extent of the inspection portion. Thus, any change in the polarization state of the light emerging from the container will necessarily be due to a birefringence effect of the material traversed; therefore, anomalies in the measured polarization property will be related to stress defects in the material, and not to refraction.To achieve this, it will suffice to order the two-dimensional 16c array of liquid crystal cells in such a way that the polarized light emitted from each of the liquid crystal cells has an identical polarization for all elementary emitting areas 16s(i,j) of the inspection portion.

[0230] From the complementary master image IM' thus acquired, at least one stress image for the inspected area of ​​the container can be calculated by computer. This stress image is obtained by calculating, for the elementary areas of the inspected area of ​​the container, a phase-shift pixel Pd(n) which corresponds to each elementary area of ​​the inspected area of ​​the container (therefore corresponding to a composite pixel Pc(n) in the case of using a digital polarimetric camera 18) and whose value is representative of a polarization phase shift <p(n), induit, par une contrainte mécanique résiduelle située dans la zone élémentaire du récipient correspondant au pixel composite pc(n), lumière émergente émanant de cette récipient. on comprend que valeur d’un déphasage pd(n) induit est donc image l’intensité des contraintes mécaniques résiduelles le matériau

[0231] To achieve this, a simple solution, when, as in Figure 1, the system 10 does not include a quarter-wave delay plate in the light path, is to ensure that the liquid crystal cells are held at rest, with zero voltage control. When the liquid crystal cell technology is of the "TN" type, the cells generally cause, at rest, a 90° rotation of the linear polarization axis direction, thus an angular shift of the orientation ©s(i,j) = 90° with respect to the polarization axis A0 defined by the upstream linear polarizer. Thus, the emitted light is linearly polarized at 90° to the direction of the polarization axis A0 of the upstream linear polarizer over the entire inspection portion of the emitting surface 16s.When liquid crystal cell technology allows a phase shift ^16X4 j) to be controlled between the two orthogonal components of the electric field vector of light, as for example with a . ECB-type technology, it is controlled at the maximum voltage to suppress birefringence, and since no birefringence is created, and therefore no phase shift, the emitted light is linearly polarized in the direction of the polarization axis AO of the upstream linear polarizer 16b over the entire inspection portion of the emitting surface 16s. In both cases, the light incident on the container 12 is, at all points, linearly polarized light with a common polarization axis. Similarly, with a system including a quarter-wave delay plate 16d in the illumination device 16, this quarter-wave delay plate 16d having a fast axis parallel to the polarization axis AO defined by the upstream linear polarizer 16b, for example as illustrated in [Fig.2], it leaves the emitted light linearly polarized over the entire inspection portion of the emitting surface 16s parallel or orthogonally to the polarization direction of the upstream linear polarizer 16b. .

[0232] In this case, a phase-shift image can be calculated in which the calculation of each phase-shift pixel Pd(n) corresponding to an elementary zone of the container is performed based on the value of at least the partial pixel Pp'2(n) corresponding to the elementary zone of the container and appearing in the first complementary partial image IP'2 associated with the linear analyzer having its polarization axis A2 perpendicular to the polarization axis AO of the incident light. For example, each phase-shift pixel Pd(n) is equal to the value of the partial pixel Pp'2(n), with therefore: Pd(n) = Pp'2(n).

[0233] Figure 3 illustrates a configuration that can be used to implement another method of creating the stress image, which consists of using circularly polarized incident light and analyzing it by filtering the light emerging from the container 12 using the quarter-wave delay plate 34. Liquid crystal cell technology is used, allowing control of the birefringence of the cells to create a phase shift between the two orthogonal components of the electric field vector of the light, for example with ECB-type technology. The two-dimensional array 16c of liquid crystal cells is controlled such that the polarized light from each of the liquid crystal cells has the same phase shift. <pi6c(iy j) entre les deux composantes orthogonales du vecteur de champ électrique la lumière issue cellule à cristaux liquides, identique pour toutes cellules. les cellules ecb ont une biréfringence variable selon commande et se comportent comme lame retard dont l’axe rapide est 45° direction polarisation linéaire amont ao le peut être modifié par tension appliquée chaque cellule, correspondre un quart longueur d’onde, ce qui induit déphasage (pi 6<l, 90 degrés d’angle. puisque ao, émise polarisée circulairement sur toute portion d’inspection surface émettrice 16s.

[0234] The case is described where the system includes a quarter-wave delay plate 34 downstream of the inspection location 13, this quarter-wave delay plate 34 having a fast axis parallel to the polarization axis AO defined by the upstream linear polarizer 16b, as in the example of [Fig. 3] which also implements a polarimetric camera. Since the A1 axis is parallel to the polarization axis AO of the upstream linear polarizer 16b, the quarter-wave delay plate 34 has a fast axis parallel to the polarization axis A1 of the individual polarizing filters 30(n,1), therefore at -45 degrees angle to the polarization axis A3 of the individual polarizing filter 30(n,3), at +45 degrees angle to the polarization axis A4 of the individual polarizing filter 30(n,4).In such a case, in the absence of any change in the polarization of the incident light due to a stress defect, the light transmitted by the quarter-wave delay plate 34 becomes linearly polarized along a downstream linear polarization direction orthogonal to the polarization axis A4 and parallel to the polarization axis A3, so that the partial pixel Pp'4(n) is zero, i.e., there is extinction. In the presence of a change in the polarization of the incident light due to a stress defect, the light transmitted by the quarter-wave delay plate 34 becomes linearly polarized along a downstream linear polarization direction not orthogonal to the polarization axis A4, so that the partial pixel Pp'4(n) is normally non-zero with a value that depends on the stress.

[0235] In this case, the computer calculation of each phase shift pixel Pd(n) corresponding to an elementary zone of the container 12 is carried out from the value of at least the partial pixel Pp'4(n), and possibly also from the value of the partial pixel Pp'3(n) which correspond to the elementary zone of the container and which appear in the complementary partial images IP'4, IP'3 associated with the linear analyzer 30(n,4), 30(n, 3) having their polarization axis at 45 degrees angle from the fast axis of quarter-wave delay plate 34, therefore at 45 degrees angle from the polarization axis AO of the incident light.Preferably, the computer calculation of each phase shift pixel Pd(n) corresponding to an elementary zone of the container is performed from the value of the two partial pixels Pp'4(n) and Pp'3(n) which correspond to the elementary zone of the container and which appear in the two complementary partial images IP'4, IP'3 each associated with the linear analyzers having their polarization axes at a 45-degree angle to the fast axis of the quarter-wave delay plate 34, in one direction or the other. Under these conditions, a first formula for calculating a value of each phase shift pixel Pd(n) corresponding to an elementary zone of the container can be written: .

[0236] [Math. 10] Pd(n) = 2arctanJÿ'^

[0237] Under the same conditions, a second formula for calculating the value of each pixel with phase shift Pd(n) corresponding to an elementary zone of the container can be written:

[0238] [Math. 11] Pd(n) = arcos(Pp'3(n) -Pp'4(n))

[0239] In the case where circularly polarized emitted light and a quarter-wave retarder plate are in front of the polarimetric camera lens, the calculation according to equation Math 11 above provides an isotropic measurement of stress defects with a sensitivity that depends on the strength of the internal mechanical stresses. The two-dimensional stress image containing the phase-shift pixels Pd(n) can be analyzed by any known image processing method, such as high-pass filters, gradients, comparisons of pixels with the average of neighboring pixels in the stress image, or comparisons of the phase-shift pixels Pd(n) to a reference phase-shift value corresponding to a maximum tolerated stress.

[0240] Regardless of the polarization properties of the emitted light, an intensity image It can be calculated from at least two partial images or a master image, in which the value of each intensity pixel Pt(n) represents only the intensity of light emerging from an elementary zone of the inspected area of ​​the container and thus primarily represents the absorption of light that has passed through at least one wall of the container 12. The value of each intensity pixel Pt(n) is calculated as an average value of the values ​​of at least two partial pixels Pp'l(n), Pp'2(n) corresponding to the same elementary zone of the container in at least one pair of two complementary partial digital images for which the polarization axes A1, A2 of the linear analyzers are orthogonal to each other. The detection of any local intensity anomaly makes it possible to detect primarily light-absorbing defects.Thus, the value of each pixel of intensity Pt(n) of the image of intensity It can therefore be calculated for example in the form: . Pt(n) = Pp'l(n) + Pp'2(n).

[0241] If a polarimetric digital camera 18 is used, from a single master image IM or IM', four partial digital images can be obtained, corresponding to two pairs (A1, A2) and (A3, A4) of orthogonal polarization axes, the two pairs being offset from each other by an angle of 45 degrees. In this case, the value of each intensity pixel Pt(n) of the intensity image can also be calculated by following one of the following formulas: Pt(n) = Pp3(n) + Pp4(n), or Pt(n) = Pp'3(n) + Pp'4(n), or Pt(n) = Ppl(n) + Pp2(n) + Pp3(n) + Pp4(n), or Pt(n) = Pp'l(n) + Pp'2(n) + Pp'3(n) + Pp'4(n)

[0242] In this text, an averaged value may be, for example, an arithmetic mean or other, weighted or unweighted, etc. For example, as in the examples given above, an averaged value of two values ​​may be the sum of these two values.

[0243] The intensity image It can be calculated regardless of the polarization properties of the emitted light, therefore with a variation of the property in the DI direction or in the D2 direction, or without a variation of the property, as intended to obtain the stress image. It can be calculated from any master image IM or complementary master image IM'.

[0244] The intensity image It containing the intensity pixels Pt(n) can be analyzed by any known means of image processing, such as those described above (for example, spatial high-pass filters, gradients, comparisons of pixels with the average of neighboring pixels in the intensity image, etc.) to detect in particular light-absorbing defects.

[0245] In other words, we can: - control the light source so that the emitting surface 16s produces light with a variation in polarization properties along the direction Dl, - acquire a master IM image, - calculate a raw IR1 refraction image and deduce an IAR1 refraction analysis image to identify refractive defects; - Based on the same master image IM, calculate an intensity image It to identify absorption defects.

[0246] Furthermore, for a given inspected area of ​​a given container, the phase shift image ID and the intensity image It can be calculated from the same single complementary master image IM' acquired by a digital polarimetric camera 18. This complementary master image IM' can be acquired with the same digital polarimetric camera 18, and with the same illumination device 16 as that used to acquire the master image IM used to calculate the raw refraction image IRm as defined above. However, this complementary master image IM' is acquired at a time that is different from the time of acquisition of the master image IM used to calculate the raw refraction image IRm with the same digital polarimetric camera 18, and with the same illumination device 16.Between the two acquisition times, the two-dimensional 16c array of liquid crystal cells is commanded to switch from one to the other of two configurations among: . - a refraction acquisition configuration in which, on the primary inspection portion of the emitting surface, a triangular variation of the induced phase shift (pl6c(L j)) is obtained along a primary direction Dl of the emitting surface, in a light initially linearly polarized by the liquid crystal cell 16c(i,j) which it passes through, as a function of the position of the elementary emitting zone along the primary direction Dl, this triangular variation exhibiting several successive primary periods with such a triangular variation of the polarization property as a function of the position of the elementary emitting zone 16s(i,j) along the primary direction Dl. - and a stress acquisition configuration in which, for all 16c(i,j) liquid crystal cells of the two-dimensional 16c matrix, a common value of the phase shift is obtained <pl 6c(i. j) induit, dans une lumière initialement polarisée linéairement, par la cellule à cristaux liquides 16c(i,j) qu’elle traverse, lors de l’acquisition ou des images complémentaires.

[0247] Thus, with the same system 10 comprising a single polarimetric camera and a single illumination device, at least three distinct images can be calculated containing information respectively related to: - to the refraction induced by the container in the light emerging from each elementary zone of the inspected area, - to the absorption induced by the container in the light emerging from each elementary zone of the inspected area, - to internal mechanical stresses in the container material, for each elementary zone of the inspected area.

[0248] With a system 10 having a single illumination device comprising a two-dimensional 16c array of liquid crystal cells and a single polarimetric camera, two or three master images can be acquired and three or four images can be calculated from among: - a refracted image along a direction Dl; - an image of intensity; - a refracted image along a direction D2 different from Dl, for example perpendicular to Dl; - an image of stress.

[0249] In the present text, therefore in all pixel calculations used in this invention, the calculated pixel values ​​can obviously be coded in floating point or normalized to be brought back to numerical values ​​for example on 8 or 16 or 24 bits.< / pl>

Claims

Claims

1. Opto-computer method for inspecting in through light a glass container (12) moving along a movement trajectory (T), in which: - the method comprises illuminating the container (12) by an illumination device (16) comprising at least one two-dimensional emitting surface (16s), which is arranged on one side of the movement path and which is made up of elementary emitting zones each emitting polarized emitted light having an emitted polarization property of interest which varies according to a periodic variation law as a function of the position of the elementary emitting zone in the emitting surface; - the method comprises observing the container (12), by at least one digital camera (18, 18.1, 18.2) having a two-dimensional photoelectric sensor (22) comprising photoelectric elements which each comprise a photoelectric cell corresponding to a pixel in an image acquired by the digital camera, the at least one digital camera (18, 18.1, 18.2) being located, relative to the movement path (T), on the side opposite that of the illumination device (16), so as to collect, by the at least one digital camera, an emergent light emanating from the container (12) and having passed through at least one wall thickness of the container; - the method comprises the acquisition, with the at least one camera (18, 18.1, 18.2), of partial digital images (Ipk.m), each containing an image of the same inspected area of ​​the container (12), each partial digital image (Ipk.m) having N partial pixels (Ppk.m(n)) each of which is the image of a corresponding elementary area of ​​the container (12), and each partial digital image being acquired with the interposition, between the container and the photoelectric cells of the at least one camera, of a linear analyzer (30(n,k); 30.1, 30.2) having a given polarization axis (Ak) for a partial digital image (Ipk.m); - the acquisition comprises the acquisition of at least one series (SI, S2, Sm) comprising at least a first partial digital image (Ipl.l, Ipl.2, Ipl.m) and a second partial digital image (Ip2.1, Ip2.2, Ip2.m), for which the polarization axes (Ak) of the linear analyzers are distinct from each other, the partial digital images

2. (Ipk.m) of the same series (Sm) being superimposable such that each elementary zone of the inspected zone of the container (12) is imaged by a corresponding partial pixel (Ppk.m(n)) in each of the partial digital images (IPk.m) of the series (Sm); - for a primary series (SI), the partial digital images (Ipk.l) of the primary series (SI) each contain, in the background, the image of the same primary inspection portion of the emitting surface (16s), the primary inspection portion being observed through the container by the digital camera (18, 18.1, 18.2), and, on the primary inspection portion of the emitting surface (16s), the law of periodic variation of the emitted polarization property of interest presenting, in a primary direction (Dl), a primary periodic variation, and presenting several primary periods (Tl) over the extent of the primary inspection portion in the primary direction (Dl); characterized in that, over a primary period (Tl), the polarization property of interest emitted by the lights emitted by the elementary emitting zones of the primary inspection portion of the emitting surface (16s) follows a triangular variation as a function of the position of the elementary emitting zone in the primary direction (Dl), and in that the method comprises the computer calculation of at least one raw primary refraction image (IR1), from the partial digital images of the primary series, by calculating, for each of the elementary zones of an inspected zone of the container (12), a raw primary refraction pixel (Prl(n)) whose value is representative of the refraction undergone by the light having passed through at least one wall thickness of the container (12) and emerging from the elementary zone, from the value of the corresponding partial pixels (Ppk.l(n)) which are the image of the elementary zone in the partial digital images (IPk.l) of the primary series. Method according to claim 1, characterized in that, for the same inspected area of ​​the same container (12), the method comprises the acquisition, for the primary series (SI), of a third partial digital image (IP3.1) and a fourth partial digital image (IP4.1) for which the polarization axes (A3, A4) of the linear analyzers (30(n,k)) are distinct from each other and distinct from the polarization axes (A1, A2) of the linear analyzers (30(n,k)) for the first partial digital image (IP1.1) and the second partial digital image (IP2.1) of the primary series (SI), preferably or-

3.

4.

5. thogonal to each other and offset by 45 degrees of angle of the polarization axes (Al, A2) of the linear analyzers for the first partial digital image (IP1.1) and the second partial digital image (IP2.2) of the primary series (SI). Method according to any one of claims 1 or 2, characterized in that, for the same inspected area of ​​the same container (12), the acquisition comprises the acquisition of at least one secondary series (S2) of partial digital images (Ipk.2); - in that, for the secondary series (S2), the partial digital images (Ipk.2) each contain, in the background, the image of the same secondary inspection portion of the emitting surface (16s), the secondary inspection portion being observed through the container (12) by the digital camera (18, 18.1, 18.2), and, on the secondary inspection portion of the emitting surface, the law of periodic variation of the emitted polarization property of interest having, in a secondary direction (D2) of the emitting surface, different from the primary direction (Dl), a secondary periodic variation, and having several secondary periods (T2) over the extent of the secondary inspection portion in the secondary direction; - in that, over a secondary period (T2), the polarization property of interest emitted by the lights emitted by the elementary emitting zones of the secondary inspection portion of the emitting surface follows a triangular variation as a function of the position of the elementary emitting zone along the secondary direction (D2), and in that the method comprises the computer calculation of at least one secondary raw refraction image (IR2), from the partial digital images of the secondary series (S2), by calculating, for each of the elementary zones of an inspected zone of the container (12), a secondary raw refraction pixel (Pr2(n)) whose value is representative of the refraction undergone by the light having passed through at least one wall thickness of the container (12) and emerging from the elementary zone, from the value of the corresponding partial pixels (Ppk.2(n)) which are the image of the elementary zone in the partial digital images (IPk.2) of the secondary series (S2). Method according to any one of the preceding claims, characterized in that the partial digital images (Ipk.m) of the same series (Sm) are acquired at the same time. A method according to any preceding claim, wherein

6.

7. characterized in that the at least one digital camera is a polarimetric digital camera (18), having a two-dimensional photoelectric sensor (22) comprising photoelectric elements (26(n,l)) which each comprise a photoelectric cell (28(n,k)) in front of which is arranged an individual linear analyzer (30(n,k)) associated with the photoelectric cell (28(n,k)) of this photoelectric element (26(n,k), the photoelectric sensor (22) comprising a number N of distinct groups (26(n)) of 4 contiguous photoelectric elements (26(n,k)) whose individual linear analyzers (30(n,k)) each have a polarization axis (Ak), the four polarization axes (Ak) of a given group (26(n)) of 4 photoelectric elements (26(n,k)) forming two pairs ((A1, A2), (A3, A4)) of orthogonal polarization axes, the two pairs being offset from each other by 45 degrees of angle; - and in that the acquisition of the 4 partial digital images (Ipk.m) of the same series (Sm) is carried out, with the photoelectric sensor (22) of the polarimetric camera (18), by the acquisition of a master digital image (IM.m) containing an image of the container (12), the master digital image (IM.m) having a number 4*N of master pixels grouped into N composite pixels each corresponding to a group of contiguous photoelectric elements, each composite pixel having 4 master pixels each corresponding to one of the elements (26(n,k)) of the group (26(n)) of contiguous photoelectric elements corresponding to this composite pixel, and each master digital image (IM.m) comprising the 4 separate partial digital images (IPk.m) each having N partial pixels (Ppk.m(n)), the partial pixels (Ppk.m(n)) of each of the partial digital images (IPk.m) corresponding, for a partial digital image (IPk.m) given, to the photoelectric elements (26(n,k)) of the photoelectric sensor (22) whose individual linear analyzers (30(n,k)) have a common polarization axis (Ak) for this partial digital image (IPk.m). Method according to any one of the preceding claims taken in combination with claim 3, characterized in that, for the same inspected area of ​​the same container, the primary series of partial digital images and the secondary series of partial digital images are acquired at different times. Method according to any one of the preceding claims taken in combination with claim 3, characterized in that, for the same inspected zone of the same container (12), the primary series (SI) of partial digital images (IPk.l) and the secondary series (S2) of partial digital images (IPk.2) are acquired with the same at least one digital camera (18, 18.1, 18.2).

8. Method according to any one of the preceding claims taken in combination with claim 3, characterized in that the primary inspection portion and the secondary inspection portion correspond to two different polarization states, at different times, of the same inspection portion of the emitting surface (16s).

9. Method according to any one of the preceding claims, characterized in that the triangular variation is such that each primary period (Tl) is divided into only two parts (Tic, Tld), an increasing part (Tic) and a decreasing part, in that, in the increasing part, the emitted polarization property of interest is an increasing linear function of the position of the elementary emitting zone according to the primary direction (Dl), the emitted polarization property of interest increasing from a lower primary value (P 1min) to a higher primary value (Plmax), and in that, in the decreasing part (Tld), the emitted polarization property of interest is a decreasing linear function of the position of the elementary emitting zone according to the primary direction (Dl), the emitted polarization property of interest decreasing from the upper primary value (Plmax) to the lower primary value (P 1min).

10. Method according to claim 9, characterized in that the increasing part (Tic) and the decreasing part (Tld) of each primary period (Tl) are of equal extent along the primary direction (Dl).

11. Method according to any one of the preceding claims, characterized in that the inspection portion of the emitting surface (16s) is made up of elementary emitting zones each emitting elliptically polarized emitted light having an ellipticity ratio less than or equal to 0.7, and in that the polarization property of interest emitted from the light emitted by an elementary emitting zone is the orientation (0s(i, j)) of the main axis of polarization of the light emitted by said elementary emitting zone.

12. Method according to claim 11, characterized in that the lower, respectively higher, value of the emitted polarization property of interest is an angular value lower over a period, respectively higher over a period, of the orientation of the axis main polarization of the light emitted by the elementary emitting zones, the angular difference between the upper angular value and the lower angular value being at least 45 degrees of angle, preferably at least 70 degrees of angle.

13. Method according to any one of claims 1 to 10, characterized in that the primary inspection portion of the emitting surface (16s) is made up of elementary emitting zones each emitting emitted light polarized according to an elliptical polarization having a phase shift (¢)16s(i, / )) between the two orthogonal components of the electric field vector of the polarized emitted light, and in that the emitted polarization property of interest corresponds to the phase shift ( ¢)165(4 / )) between the two orthogonal components of the electric field vector of the polarized emitted light.

14. Method according to any one of the preceding claims, characterized in that the primary period is seen by the two-dimensional photoelectric sensor (22) with a resolution, in the primary direction (Dl), of at least 15 partial pixels of the same partial digital image per primary period.

15. Method according to any one of the preceding claims, characterized in that the inspected area of ​​the container is seen by the two-dimensional photoelectric sensor (22) with a resolution, in the primary direction, of at least 5 partial pixels of the same partial digital image per millimeter on the container.

16. Method according to any one of the preceding claims, characterized in that the value of a raw refraction pixel (Prm(n)) is calculated, for an elementary zone of the container (12), from the arc-tangent of a ratio between the values ​​of two corresponding partial pixels (Ppk.m(n)) in the first partial image (IPl.m) and the second partial image (IP2.m).

17. Method according to any one of claims 1 to 15, taken in combination with claim 2, characterized in that the value of a raw refraction pixel (Prm(n)) is calculated, for an elementary zone of the container (12), from Parc-tangent of a ratio between, on the one hand, the difference in value of two corresponding partial pixels (Ppk.m(n)) in the first partial image (IPl.m) and the second partial image (IP2.m), and, on the other hand, the difference in value of the two corresponding partial pixels (Ppk.m(n)) in the third partial image (IP3.m) and the fourth partial image (IP4.m).

18. Method according to any one of the preceding claims, characterized in that the illumination device (16) comprises, in the direction of propagation of the light, a primary two-dimensional source (16a) of diffuse light, an upstream linear polarizer (16b) having a polarization axis (AO), and a two-dimensional matrix (16c) of liquid crystal cells (16c(i,j)).

19. Method according to claim 18, characterized in that it comprises controlling the two-dimensional matrix (16c) of liquid crystal cells such that the polarized light from each of the liquid crystal cells (16c(i,j)) has an elliptical polarization having, for each liquid crystal cell (16c(i,j)), the orientation ( 0C(i,J) ) of the main axis of polarization and / or a phase shift ( ^>16c(z,j)) between the two orthogonal components of the electric field vector of the light from the liquid crystal cell (16c(i,j)), and in that, for the acquisition of the primary series (SI) of partial digital images (IPk.l), at least one of the orientation (0c(i, / ) ) of the main axis of polarization and / or the phase shift (tpl6c(i,j)) follows a triangular variation depending on the position of the liquid crystal cell ( 16c(i,j)) along the primary direction (Dl).

20. Method according to claim 19 taken in combination with claim 3, characterized in that it comprises the control of the two-dimensional matrix (16c) of liquid crystal cells in such a way that, for the acquisition of the secondary series (S2) of partial digital images (IPk.2), at least one of the orientation (0c( / . / j ) of the main axis of polarization and / or the phase shift ((pI6c(i, / )) follows a triangular variation as a function of the position of the liquid crystal cell (16c(i,j)) in the secondary direction (D2).

21. Method according to claim 20, characterized in that it comprises the control of the two-dimensional matrix (16c) of liquid crystal cells in such a way that, successively, for the acquisition of the primary series (SI) of partial digital images (IPk.l) of a given container (12), at least one of the orientation (0c (i, j)) of the main axis of polarization and / or the phase shift ( <pl6c(i, j)) suit une variation triangulaire en fonction de la position de la cellule à cristaux liquides ( 16c(i,j)) selon la direction primaire (Dl), puis de telle sorte que, pour l’acquisition la série secondaire (S2) d’images numériques partielles (IPk.2), at least one of the orientation (0c( i, / )) of the main polarization axis and / or the phase shift (ç?l 6c(4 j)) follows a triangular variation depending on the position of the liquid crystal cell ( 16c(i,j)) according to the secondary direction (D2).

22. Method according to any one of the preceding claims, characterized in that it comprises a prior step of calibrating the control of the two-dimensional matrix (16c) of liquid crystal cells.

23. Method according to any one of the preceding claims, characterized in that it comprises a step of analyzing refractive anomalies comprising a step of computer calculation on the basis of the raw refraction image.

24. Method according to claim 23, characterized in that the step of analyzing refractive anomalies comprises a step of detecting a gradient in the raw primary refraction image (IRl.m) along the primary direction (Dl).

25. Opto-computer system (10) for inspection in through light, using at least one digital camera (18), of a glass container (12) moving along a movement path (T), in which: - the system comprises an illumination device (16) comprising at least one two-dimensional emitting surface (16s), arranged on one side of the movement path and which is made up of elementary emitting zones each emitting polarized emitted light having a polarization property; - the system comprises at least one digital camera having a two-dimensional photoelectric sensor (22) comprising photoelectric elements which each comprise a photoelectric cell, the at least one digital camera (18, 18.1, 18.2), being located, with respect to the movement path (T), on the side opposite that of the illumination device (16), so as to collect, by the at least one digital camera, an emergent light emanating from the container (12) and having passed through at least one wall thickness of the container; - the system (10) is configured to acquire, with the at least one digital camera (18, 18.1, 18.2), at least one series (Sm) comprising two partial digital images (IPl.m, IP2.m, IPk.m), each containing an image of the same inspected area of ​​the container (12), each partial digital image (IPk.m) having N partial pixels. (Ppk.m(n)) each of which is the image of a corresponding elementary zone of the container (12), and each partial digital image (IPk.m) being acquired with interposition, between the container (12) and the photoelectric cells (28(n,k)) of the at least one digital camera (18, 18.1, 18.2), of a linear analyzer (30(n,k), 30.1, 30.2) having a given polarization axis (Ak) for a partial digital image (Ipk.m), the polarization axes (Ak) of the linear analyzers (30(n,k), 30.1, 30.2) for the at least two partial digital images (IPl.m, IP2.m, IPk.m) being distinct from each other, the partial digital images (IPl.m, IP2.m, IPk.m) of the same series (Sm) being superimposable such that each elementary area of ​​the inspected area of ​​the container (12) is imaged by a partial pixel (Ppk.m(n)) corresponding in each of the partial digital images (IPl.m, IP2.m, IPk.m) of the series (Sm); characterized in that the illumination device (16) comprises, in the direction of propagation of the light, a primary two-dimensional source (16a) of diffuse light, an upstream linear polarizer (16b) having a polarization axis (AO), and a two-dimensional matrix (16c) of liquid crystal cells, the system (10) comprising control means (100) for controlling the two-dimensional matrix (16c) of liquid crystal cells such that the polarized light coming from each of the liquid crystal cells (16c(i,j)) has an elliptical polarization having, for each liquid crystal cell (16c(i,j)), an orientation (0c( / , j) ) of the main axis of polarization and / or a phase shift {(pi 6c(i, j)) between the two orthogonal components of the electric field vector of the light coming from the liquid crystal cell (16c(i,j)), and in that the device illumination (16) is controlled such that at least one of the orientation (0c( i,j ) ) of the main axis of polarization and / or the phase shift ( <pl 6c(i, j)) suit une variation en fonction de la position de la cellule à cristaux liquides ( 16c(i,j)) selon une direction primaire de la surface émettrice (16s), the illumination device (16) is controlled such that at least one of the orientation (0c ( i, j) ) of the main polarization axis and / or the phase shift (tp16c(i, y)) follows a triangular variation as a function of the position of the liquid crystal cell ( 16c(i,j)) along a primary direction of the emitting surface (16s).

26. System according to claim 25, characterized in that it comprises, in the path of the light between the two-dimensional matrix (16c) of liquid crystal cells and the linear analyzers (30(n,k), 30.1, 30.2) for the at least two partial digital images (IPl.m, IP2.m, IPk.m), a quarter-wave delay plate (16d, 34) which has a fast axis oriented parallel or perpendicular to the polarization axis (AO) of the upstream linear polarizer (16b).

27. ​​A system according to claim 26, characterized in that the quarter-wave delay plate (16d) is arranged in the light path between the two-dimensional matrix (16c) of liquid crystal cells and the container (12).

28. System according to claim 26, characterized in that the quarter-wave delay plate (34) is arranged in the light path between the container (12) and the linear analyzers (30(n,k), 30.1, 30.2) for the at least two partial digital images (IPl.m, IP2.m, IPk.m).

29. System according to any one of claims 25 to 28, characterized in that it comprises a computer calculation unit (110) programmed to carry out the computer calculation of at least one raw primary refraction image (IRm), from the partial digital images (Ipk.m), by calculating, for each of the elementary zones of an inspected zone of the container (12), a refraction pixel (Prm(n)) whose value is representative of the refraction undergone by the light having passed through at least one wall thickness of the container (12) and emerging from the elementary zone, from the value of the corresponding partial pixels (Ppk.m(n)) which are the image of the elementary zone in the partial digital images (Ipk.m).

30. System according to any one of claims 25 to 29, characterized in that the digital camera is a polarimetric digital camera (18), having a two-dimensional photoelectric sensor (22) comprising photoelectric elements (26(n,k)) which each comprise a photoelectric cell (28(n,k) in front of which is arranged an individual linear analyzer (30(n,k)) associated with the photoelectric cell (28(n,k) of this photoelectric element, the photoelectric sensor (22) comprising a number N of distinct groups of 4 contiguous photoelectric elements (26(n,k)) whose individual linear analyzers (30(n,k)) each have a polarization axis (Ak), the four polarization axes (Ak) of a given group of 4 photoelectric elements forming two pairs ((A1, A2), (A3, A4)) of polarization axes (Ak) orthogonal polarization, the two pairs being offset from each other by 45 degrees of angle.

31. System according to any one of claims 25 to 30, taken in combination with claim 25, characterized in that the control of the two-dimensional matrix (16c) of liquid crystal cells is synchronized with the acquisition, with the at least one camera (18, 18.1, 18.2), of the at least two partial digital images (IPl.m, IP2.m, IPk.m) so as to: - acquiring a primary series (SI) of at least two partial digital images (IP1.1, IP2.1, IPk.l) when the two-dimensional matrix (16c) of liquid crystal cells is controlled such that at least one of the orientation (0c (z, j)) of the main polarization axis and the phase shift (ç>16c(z, j)) follows a triangular variation as a function of the position of the liquid crystal cell (16c(i,j)) along the primary direction (Dl); - acquiring a secondary series (S2) of at least two partial digital images (IPI.2, IP2.2, IPk.2) when the two-dimensional matrix (16c) of liquid crystal cells is controlled such that at least one of the orientation (0c (z, j)) of the main polarization axis and the phase shift (ç>16c(z, j)) follows a triangular variation as a function of the position of the liquid crystal cell (16c(i,j)) in a secondary direction different from the primary direction.

32. System according to any one of claims 25 to 31, characterized in that the polarization axes (Al, A2) of the linear analyzers (30(n,k), 30.1, 30.2) for the at least two partial digital images (IPl.m, IP2.m) are orthogonal to each other.

Images